The issue, I think, with 'change healing requirements' as being the entire solution, is that A: it would take so much more work to rebalance, recheck, make sure everything still works correctly re: old content, and B: it only solves the problem with specific gear levels. Take the aforementioned EX roulette dungeon mobs, that spammed raidwide damage. When we first encountered them, in our new lv100 AF gear at i690, they hurt, quite a lot. Many took to the forums, reddit etc to say 'this is great, we have to actually heal again' because we had trouble keeping up without using GCDs. Fast forward... literally a week? To when we had i700, and suddenly we didn't need to GCD heal anymore. Then another couple of weeks later, we have i710 crafted/normal raid gear, and we're healing it like it's just another EW dungeon. The speed at which we outpace 'challenge via how much we have to heal' due to our gear upgrading, is simply too fast IMO to be a viable solution.
That's not to say that it (increasing healing requirements) can't be a part of the solution (hence why I included some extra healing options in the designs, because I'd assume SE would increase healing requirements a bit alongside such designs), but I don't think it can be the whole solution. Because once we figure out 'how much healing is needed', we go back to the current damage that so many are not happy with. I don't think it'd solve anything, to go from 100% of my GCDs in a dungeon on trash (as, say, SCH) being damage, to 70% (because I'm required to press Adlo/Succor occasionally), because those 70% are still just going to be Art of War. Rather, having a situation where the skilled player can reach 100% damage GCDs again, and those damage GCDs being more varied, but a less skilled player finding their 1-button damage gameplay being broken up by pressing Adlo/Succor instead, would be the better solution I think. It gives the learning player a goal to strive for (swap out Adlos for Art of Wars, and Succors for Shadowflares, etc), and a player that has learned, something as a reward structure of sorts for their knowledge (having a variety of actions to use for damage). The 'variety' in buttons pressed when they're damage buttons, is also 'gear agnostic', it would not matter if the player was i690 or i730 in the Tender Valley if there were more variety in damage buttons to press, as they'd be able to interact with that button variety regardless of gear level, whereas with 'heal more', that might be true at i690, but maybe they don't need to GCD heal at all (even with increased healing requirements) at i730, and so they'd be in the same situation as now, where their GCD gameplay is back to being a single button
I did some maths back in Endwalker's 6.5, when Aetherfont was still a current dungeon of EX roulette. And IIRC, to get the first boss (the axolotl (?) looking thing) to deal enough damage to put me, a BIS SCH, in a situation where I'd have to use even a single GCD heal, it'd have to have done a raidwide for 20k damage, every 15ish seconds, on top of what it already was doing. I could go do the same maths for DT dungeons (eg the new one), but thanks to stuff like Divine Aura (1000p of regen) it's even more difficult to burden the kits. The sheer amount of healing potency we can blast out is honestly obscene, and I'm not sure how much work it'd take to get us into a situation where the incoming damage justifies the kit's power. Even if it were possible, I'd expect it'd cause less skilled players to be unable to keep up, and cause player friction, and we know SE hates player friction.