To the first: I consider things by their effects. IF MP MANAGEMENT WAS an issue in this game, then MP cost would be a valid consideration. But it isn't, and likely won't be again unless/until they do a large revamp of the combat system. If healer MP becomes an issue, then people will have legitimate reasons to not cast Glare/Dia/etc, which the Devs have decided they don't want (granted, they could just make those spells cost no MP, but they likely won't do that, either). Besides which, effect determines use case. For the sake of argument, suppose we had Medica 2 costing 1k MP, 2 sec base cast, 2.5 sec GCD, having a 250 potency cure and a 15 second 100 potency Regen (same as today). Suppose we had Solace as a 2 sec base cast, 2.5 sec GCD, having a 250 potency cure and a 15 second 100 potency Regen. Suppose we had some kind of CD that also consumed 2 seconds of the GCD window somehow, and likewise had the same stats.
In practice, they'd all fill exactly the same use, which is amazingly boring imo because the distinction is just based on resource cost, and MP is never a limiting resource unless you're chain casting Raise.
In live, you use Lilies over MP costing GCDs because they're instant cast and refund the lost damage of a foregone Glare, not because their MP cost is 0 instead of 1,000. If Medica 2 (or even 1) generated a Blood Lily and was instant cast, people would probably use those spells somewhat frequently as well. And you don't always use Lilies for movement (that's an additional use case that just makes Medicas even more irrelevant). If, on the other hand, they had distinct effects, then it would make use to have both in your toolkit. As it is in the game right now, there's legitimately no reason for Medica 1 to exist after around level 50. Lower level content generally doesn't require chain casting AOE heals, and the first fight I remember NEEDING to do this was Niddy, which is during a stack mechanic where you have Cure 3 and use it instead.
I dunno, I may not be wording it well, but I consider the effect of spells as the deciding factor, generally. That Lilies cost no MP isn't relevant in my deciding to use one, but that they are instant and damage neutral is. PERSONALLY I'd like to see them as Regens (in whole or part) and Lilies turned more into a system you use frequently to provide continuous healing over time, but that's apparently just me.
EDIT (for space):
Consider that a lot of people play MMOs. A lot of TYPES of people play MMOs. And apparently, one type of Human is the type that likes to help others but not necessarily harm others. For example, doctors in our world do not often carry guns and shoot people. You can argue ones in war do, but it's more ones in war CAN, some genuinely choose not to (e.g. Hacksaw Ridge). These players that don't like dealing damage/harm but DO enjoy aiding friends and allies tend to pick the role called "healer".sacrificed
If you'd like to posit a guess as to why they pick such a role instead of the one called "damage dealer", I think it might be instructive for you to consider such a question.
It's not a matter of being "excused", it's that they shouldn't HAVE to.
But, given that in FFXIV it's become accepted that they must, then the solution is to have as unimposing and, more importantly, unOBTRUSIVE a piece of that as possible. Again, these people are picking the role called "healer", not the role called "damage dealer". I'm not trying to belabor the point or rub anyone's nose in it, but there are Jobs that fall under the role called "damage dealer" (quite a few of them), and these people are actively choosing NOT to pick one of the Jobs under that role. No one picking "healer" at level 1 is thinking they are picking a damage dealer, just as no one taking classes as a nurse thinks they're entering the police academy.
I'm not trying to insult anyone's intelligence or anything (honestly, I'm really not), I'm just saying more that I'm genuinely confused when people ask this question. As if it's never occurred that one might pick a "healer" role because they DON'T enjoy damage dealing, DON'T find it engaging or interesting gameplay, and DON'T want any more mental effort or practice devoted to this thing that they dislike.
To them, a two button damage "rotation" is ideal (less ideal than no damage at all, of course, but more ideal than anything more advanced) as it means they have to devote as little thought to the thing they dislike as possible while being able to focus on the things they do like. To use the example above, suppose at nursing school everyone was required to take marksmanship courses and carry a gun, including those that are averse to violence in general, may hate guns, and are pacifists. If they were given the option of one degree plan that only required one semester of firearm training vs the "standard" course that required one each semester (eight total), many nursing students would likely opt for the degree plan that only required the 1 rather than the 8, so they could minimize their interaction with the thing(s) they dislike and focus more on the thing(s) they like that drew them to nursing and that they personally deem more important and worthy of their mental energies and study.
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HOWEVER:
As I've noted before, this isn't true of everyone.
There are many people/healers that the above fits to a T. There are some that it fits to a lower-case-t. Maybe they don't like damage dealing and would prefer buffing as their support/filler gameplay, but for whom the above fits close enough.
But there are ALSO many people who that does not fit.
Ergo, my base argument:
We have 4 healers; make 4 playstyles so everyone has one that appeals to them.
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I guess my bigger question is why people wanting to change healers feel the need to FORCE them all to and for none to be approachable to players that don't like damage dealing, and, in fact, chose the role called healer explicitly to avoid it as much as possible.
I've been given a number of answers, but none are really satisfying. One is from people that want the more damage focused gameplay, but want to play WHM SPECIFICALLY. But when asked if they'd allow a different healer to remain simple, they often refuse that, too (because of course they ALSO want to play that one, I guess?), which comes across as somewhat unreasonable.
Another answer is "everyone deals damage in this game", but that's unsatisfactory as well - no one is saying to strip all damage spells from any healers, and one does not need more than even a single button to deal damage, so one retaining Glare/Dia/Misery isn't violating the "must do damage" rule.
Another is that it shouldn't be "too easy", but that's also not acceptable - difficulty is highly subjective at the best of times, but the Devs have clearly decided that is not "too" easy, as has the player base as a whole. And games SHOULD be accessible, meaning there isn't such a thing as "too easy" anyway.
Another is the belief that those players who enjoy current gameplay REALLY don't and would like it if they were forced to change and just "gave it a chance". But the thing is, if we did that with 3 of our 4 healers, they would already have that option (and most healer players DO dabble in more than one as it is), so there's no reason to force them. Further, "force" should never even be involved in the first place. Finally, because they may NOT like it, and if all 4 were changed, they wouldn't have the option to decline. It's kind of like a friend who insists you'd like their special peanut butter and pickle sandwich if only you tried it...and then refuse to eat or spend time with you unless you try one. And if you don't like it, tough, because they've replaced all meals in your home and city/etc with variations of peanut butter and pickles and if you don't, in fact, like it, too bad for you.
You mention it "fails to challenge players", but what is "challenge"? I've healed Ex4. That's pretty challenging at some parts of it. What should "a caster...be about"? And remember we're not talking about the CASTER role here, we're talking about the HEALER role here: We have three Jobs in the Caster role, which are BLM, SMN, and RDM, none of which have to juggle healing (sit DOWN Vercure spamming RDM!!) alongside their damage rotation.
You say it stresses people and that's GOOD? Many people play games to relax and chill, even when doing challenging content with friends. STRESS is not considered good. And, again, we have THREE OTHER JOBS they can get stressed out on if they wished to do so, why should all four be that way?
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I guess my issue here is you ask a question - why would people not want what you're offering? - and you explain your reasoning - because people should be stressed out and having heart attacks whenever playing videogames because that's what you enjoy and you think everyone should (I embellish, but you get the point). Your reasoning is based on what you think games SHOULD be, but we're already talking about you getting that in 3 other cases. Meaning you can get on SCH, AST, or SGE and enjoy that style of gameplay experience yourself.
But...not everyone enjoys that.
And if you have your way, there will be no place in the game for them. If 50% of healers quit, is that a positive thing?
Not for the game, nor for the community, one would think.
And if you're getting 3 out of 4 things you want, why must you get all 4 - even if it means robbing people of 4 out of 4 things that they want - to be satisfied?
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Personally, I DO like the rotation you mentioned above.
I think that would be a great system...for Sage. I've said myself a number of times SGE should have a damage rotation akin to RDM's caster phase (ignoring the melee piece) and leverage Kardia to do the lion's share of their healing, while having their GCD heals and their oGCD mitigation abilities to patch up for rotational errors or things Kardia healing isn't sufficient for. Instead of making Kardia Eos by another name, to actually make it a healing tool in truth.
SGE heals by dealing damage, and it would be neat to me if their damage rotation was more engaging and if doing it correctly meant less reliance on other healing tools. They still have GCDs as backup in cases they DIDN'T do it correctly, but imagine the system you outlined above just changing Lilies for Addersgall and where Enlight (or the equivalent of it) also generated a Addersting stack or something. Now a good SGE is rewarded for doing their rotation by more oGCD heals they can use as well as more GCD damage they can employ, and a SGE that isn't as good at their rotation has their natural AG timer and GCD heals to rely on instead. Meanwhile, WHM is left alone for the people that don't want to deal with any of that.
Everyone wins. Well, everyone except the people that demand they must have everything and everyone else must enjoy the game as they do.
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I recognize some of this sounds like a negative/insult, but I'm trying to explain it as simply and honestly as I can.
If we changed up the 3 healers but left WHM alone, I would mostly use WHM. When I felt like it, I might use SGE with the above rotation. I would probably drop SCH because I absolutely hate DoTs and the button bloat on that Job already borderline gives me a headache (note I didn't address this above, but unless we pruned a LOT of abilities, the button bloat of adding 5 damage spells to the SIMPLE healer, and presumably more to the others, would explode hotbars)
The best option, imo, is to make SCH, AST, and SGE fill different design spaces, and WHM can be left both for those who like it and as the base/anchor point. This would get the least pushback as anyone who DOES like healing today could shift to WHM (and it would easily be the most played healer at that point, since I'd wager that's more of the playerbase), and the others exist to offer varied playstyles for people that want to engage with them.
To me, the question shouldn't be "Why would people who chose to play healers not want involved DPS rotations?"
The question COULD be "Why would people who want involved DPS rotations play the healer role instead of damage dealer, which already has DNC, RDM, and SMN capable of throwing out healing, or the tank role of PLD for that matter?"
But those aren't good questions.
The question we SHOULD ask is:
"If there's an approach that gives everyone something they want and can enjoy, why should we not use that instead?"
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I've tried peanut butter and pickles - believe me, my friend that loves them wouldn't quit until I did.
I did not, in fact, find the combination all that enjoyable and have avoided partaking ever since.
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EDIT2:
Wait, I'm a bit confused here. I'm told all the time SB and further back was amazing healer gameplay. In SB, WHM functioned almost exactly as today (I know, I was there) with one key difference: They didn't have Lilies (well, they did, but they were glorified Freecure), and Misery was called Aero 3 and was cool to look at but much less powerful and couldn't be used while moving. Yes, their DoTs had to be cast more often, but so did their GCD heals. And you seem to believe casting other spells more often doesn't make more interesting gameplay, so if casting Medica more often isn't interesting gameplay, casting Aero 2 more often can't be, either, now can it?
Wow, this is an amazing bit of...I'm not even going to say what it is.And to be hoenst, this hatred towards optimization focussed healers who want to contribute as much as possible to the party sounds like envy towards people who are just better at playing this game and who you know are contributing more towards the party and are more popular with randoms and statics alike than "I just want to heal and spread love and peace uWu" healers.
No one hates optimization focused healers, and people aren't at all envious towards them. If anything, it sounds like the optimization focused folks are envious towards the ones that just enjoy the game and have fun and want to make those people as miserable as they are. Your comment reeks of the outdated elitist viewpoint that you stand on top of the bank in Orgrimmar with full Tier 3 and everyone and their grandmother (who also plays WoW) is involuntarily forced by their rapidly beating heart to stop and stare and bask in the aura of your awesomeness knowing that you're better than them, so MUCH better than them, and you're the talk of the server as you single-handedly carry your 40 man raid to clears and everyone basks in how amazing you are with your skill and contribution to the server and party. Every woman wants to date you and every man wants to be you, and so on and so forth.
It's so 2005.
People who oppose people like you do so because they don't enjoy the same gameplay you do.
There's no hate except on your part looking down your nose at them.