The problem I have with arguments like yours is the framing.
"Enjoyable" is "asinine". "Not convoluted" is "braindead". "Fun" is "boring".
Moreover, there's no "ENFORCE simple/easy jobs arbitrarily", especially when your own position is to ENFORCE complex/hard Jobs arbitrarily. This is the part that's really confusing to me. Why is it okay for your desired Job design to be forced on all Jobs and players but not the contra? Moreover, the simple side proponents aren't even arguing for ALL Jobs to be made simple, just a few.
1) NO JOB may be simple! They must ALL be complex! Anyone who says otherwise wants braindead/etc insulting and deriding language.
2) NO JOB may be allowed to have a low skill ceiling! Only braindead/etc insulting and deriding language would want that!
Here's the question that would resolve all of this fairly quickly:
WHY must all Jobs have a skill high skill ceiling?
Not "so people can improve". No WHY? Why is that important? Why is that necessary?
Secondarily, no Job's skill ceiling will be exactly equal to its skill floor no matter how simple. So ALL Jobs have a skill ceiling higher than their skill floor, even SMN. So that is the question, not "why does the skill ceiling have to be higher than the skill floor", because that's already going to be true of any and all Jobs.
There's no way to have it where "everyone can choose their happiness" on every Job. In WoW, you can get a little (not completely, but a little) closer to that because of Talents, but FFXIV doesn't have that. You can't choose talents on SMN to give you some extra DoTs or make Fester into old Fester. Those aren't options. You likewise can't choose Talents on BLM to turn it into an Ice Mage. Those aren't options.
What we CAN hope for, though, is that every ROLE has an option for people to choose their happiness on it right now. For example, I might pick SMN and be happy, Mikey might pick RDM and be happy, you might pick BLM and be happy. But if they're all BLM, only you are happy.
So what you end up with is a system where Jobs are largely constrained to a narrow skill corridor, no matter what that is. There's not a way to play BLM that's "easy" right now. You have hard and ultra-hard (if you want to go Infinite Paradox transpose lines and explode your brain with 100% movement uptime). But there's no way to play BLM that is at SMN level. There's no way to play GNB that's WAR level. There's no way to play MNK at WHM level. So the options are mostly just making a Job complex or making it not-complex. EVERY now and then the Devs stumble onto something that lets a Job be pretty simple but with quite a bit of nuance to optimize for a higher skill ceiling.
Ironically, considering how often people call RDM simple, it's the perfect and RARE example of an "easy to play WELL but with a lot of nuance to truly master". The basic concept of how the Job works is very simple to grasp and play, and you can do respectable damage just alternating your short/long casts, then rolling into your melee combo at 50/50, using the opposite Holy/Flare then Scorch, then Resolution, and popping your two oGCD attacks when they come up. On a surface level, it's very simple to play.
...then you start looking into optimization and the opener. "Why do I use Acceleration AND Swiftcast? Wait, there's a priority system between the two? I'm supposed to fit HOW MANY melee combos in the burst phase?? What's the optimal use of Acceleration? How much White/Black should I have at what time? How should I be using Manafication vs Embolden?" It's surprisingly nuanced to play at a 90-100 on it, even if the basic concept of it is far more simple. As much as it's derided, WAR has a similar situation. So does New PLD - also derided. Kinda sensing a trend here... The thing with New PLD is more that the differences are so negligible it doesn't matter and that's probably true of WAR. RDM it's not quite as true of, but relatively so.
What is absent from these conversations is WHY no Job may be ALLOWED to have a low skill ceiling.
It's said this is bad, but not WHY. "Boring" is subjective and many people find low skill ceiling Jobs engaging and fun. So that's not an answer. "No room for growth" runs into the same problem, as (a) there's at least SOME room for growth anyway and (b) again, subjective, as both not everyone finds that engaging and enjoyable anyway and different people at different skill levels may not see the growth the same way, meaning the skill ceiling/growth may not even be perceived the same way. Someone may struggle to get RDM down while another may find it child's play to master even BLM.
So WHY is the question. Not "Why should there be a simple Job", since the answer to that is obvious - having a low skill floor and ceiling Job in each role makes roles more accessible to new entrants, be they new players, new gamers, or people just wanting to dabble in a role for the first time.
No, the question is "Why - in concrete terms - should there NOT be any simple Jobs?"
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To me, having multiple levels existing is the no brainer.
SMN is easy
RDM is medium
RDM optimized is hard
BLM normal is hard
BLM transpose infinite Paradox is galaxy brain
In fact, of ALL the roles in the game right now, I think Caster is the one that actually nails this. For Tanks, GNB is a bit harder and DRK CAN be harder depending on how you look at it, but WAR is pretty easy (with a bit of nuance) and PLD is near WAR levels. There's not a galaxy brain option, and there's debatably not a hard option. Healers.......should I go into that one? Most people consider them to have, at best, super easy, easy, and maybe a medium (SCH and/or AST) option. Melee don't really have an EASY option. RPR is the closest, but is probably more of a medium, and all the Melee Jobs other than RPR have pretty high skill ceilings to really master them, with MNK being obvious but SAM also having a pretty high bar for high level play. Ranged is just weird since all three Jobs are pretty simple to pick up but medium-ish to master, with MCH being the worst to do perfect on because of how its CDs drift if not used perfectly.
Caster is the one role that has a Job at easy, medium, and hard levels of play, and BLM has the option of going up to galaxy brain level if desired.
There's nothing really wrong with this other than "hardcore players want more".
And they have BLM and FREQUENTLY avoid playing it when offered any other choice.
/sigh
It's not a "braindead casual" vs "more hardcore". It's a question of WHY what you want is actually necessary to the point it must and should be forced on everyone when even hardcore players avoid it if given the choice.
I generall don't like galaxy brain Jobs. So I just...don't play BLM. The world doesn't stop turning, the servers don't shut down. So if you don't like easy Jobs...you could just...not play SMN? Most of the other Jobs in the game are complex in various ways, and MNK and BLM offer both Melee and Caster options for the gigabrain inclined. I'm not sure what the problem is with that.
Now, if you liked Old SMN, that's fine...but that's a different argument, as me and Mikey_R have both said.
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And for the love of Hydaelyn and/or Zodiark (whichever cult you ascribe to more, of course) - stop using the term "braindead". If you can't see how that poisons the well of literally any discussion ever, sit back in your chair, consider how you'd feel if people incessantly called things you actually find fun and enjoyable braindead, and then realize that you should stop doing it.
And I get you aren't calling for everything to be Transpose lines, but you're asking for every Job to be medium or above; again, why? Why that arbitrary bar, and why for every Job with no exceptions? The people you oppose aren't calling for every Job to be easy...