Counting 123 as 'one skill' is an odd distinction to make but I'll go along with it, by that rule, NIN (barely), DRG (specifically because it's 123 combo is actually a 12345), MNK (if you were to count it's gameplay as 123s but I wouldn't), BLM, PLD depends if you count the Atonements after as part of the 123 or if they're a separate 123. Every healer fails the 'sub-30% check', SMN barely scrapes it with the 'needs 10-12 buttons' criteria. Other than that, every job I'm looking at passes the second two criteria (since they're not healers they can't pass the first). Even DRK passes, even GNB passes (unless you get really picky and say that Gnashing plus it's Continuations are all one combo). This was looking at highest ranked speedkills for this tier
Once again, this is a picture showing the current 1min rotation for WHM. You might not consider 75% of your GCDs being used on Glare as 'spam' but a lot of us sure do. While I'd consider Ty's 30% a little difficult to aim for (I'd accept maybe 40%, since BLM is roughly there with it's Fire4 cast rate), it is possible to reach said 30%. It's surprisingly simple to, designwise too. Though, maybe the fact Quake replaces Glare in my design bumps the Glare count up in Ty's eyes from 28% to like 32% and that means it fails the check too, idk
I don't think anyone's saying encounter design cannot change, I think they (at least I am) say that since encounter design HAS changed and we're now flooded with OGCD heals, to change it to a more GCD reliant system would require nuking those OGCD tools super hard, and people are never a fan of feeling like they've been made weaker. You try and convince the casual players that 'sorry, they had to make your Lilybell heal for 200 per pulse instead of 400, it's for the good of the game though cos now you'll be pressing Medica more often to cover it!', I don't think that's gonna fly well
Ok the meat of the meal:
1: Doesn't address the boredom of 'player who has any degree of competency while healing', as the 'lower values' would be so low as to be basically ignoreable. If it's an amount that novice healers can keep up with via 'GCD healing fallbacks', ie they're panicking, we could throw out Kerachole on CD and keep up on the healing because of it's regen effect. OFC you address this in point 3 though, so lets get there
2: Doesn't address etc etc. Same as point 1, the point of the 'rework' is that it has to address the engagement of all players, in all forms of content. If you keep stuff easier in lower content, then it doesn't solve the issue. We'd go from 'zero GCDs used' to 'Medica2 once per minute/per 30s, then business as usual'. If you're aiming for this random damage to be like... you need to spot heal that person asap, then it sounds like you're asking for those old style WOW raids where your job as a healer is to just whack a mole the HP bars, and people would argue about getting sniped by the Paladin using Flash of Light
3: To follow on from part 1, reducing the OGCD effectiveness is very unlikely to work out. You risk making certain old content (ultimates for example) unbeatable. The amount of 'reduction' you'd have to do would be so big, you'd almost be removing the skill entirely. Removal/heavy reduction in OGCD effectiveness also runs counter to the second point, of having more 'random damage' to react to, as OGCDs wouldn't even get to exist as your panic button. There's been times where I try to save a tank after a big hit, and cannot, because I'm trying to Solace but am GCD locked. I've said in the past, by my estimations, to get to a level of 'GCD healing is the main source' that would have a big enough effect on the game to change how we look at healing, you'd have to reduce the power level of every OGCD we currently have by at least 50%, potentially 75%. HW and SB to a lesser extent worked because we didn't have as many different OGCD heals. In HW, for example, AST had one 'OGCD heal', and it was by channeling the bubble. The buff did not stick to you back then, it had to be channeled. I saw a video by Momo about how he and his cohealer got down to 4 GCD heals in O12S and was impressed by it, because of how much tech they used (including a Super potion on every member after a certain raidwide). Now, 'clear the fight with zero GCDs used' is kinda commonplace, as a result of how many different tools we now have. Also, you say 'so they would be tuned to that end.' re: OGCD-based healers, so you've already set up for failure. Every healer except WHM is now an OGCD-based healer. If you only reduce their OGCD healing power by say... 25%, and WHM by 50%, then we get SB style WHM exclusion again