How is making tanks weaker “homogenisation”, they are already copies of each other. “Badly implemented immortality” isn’t a design paradigm. Nerfing them all roughly equally would just be a rebalance
I'd argue that tanks and healers should largely share a similar purpose of support, Tanks are already "tanks" in the fact they tank damage so well because the actual Mitigation value of tanks is absurd that plus sustain no wonder why tanks practically invalidate what little healing healers do.
Tanks aren't really "healers" but Healers aren't really "healers" both are pretty largely defined as support dps in function, as most of their role task is done with a few buttons they interact with the game in a very similar way to dps where every decision to be made should be to Solidify their damage output, as tanks have no reason to do anything other then to damage outside of clicking free defensives, Healers are in the same boat, outside of "gcd healing decision making" which practically doesn't exist if your a average or above healer.
The game is also designed in a way that's so one dimensional that you can't have Tanks that may perform a more supportive role towards the team while other tanks could have other focuses such as being a stronger main tank, good at damage (good at damage would always be hard meta in this sort of game)
I'm speaking from what I want from tanks though I personally lean to more supportive roles in general but will never really vibe with full on "mage-like" healers which is the only thing ff14 offers in terms of healers, So as a tank I actually really love the idea of using abilities that protect my team, through mitigation and healing, I don't find tanks fun if all the do is mitigate self and aggro the boss playing a largely selfish role.
Healers aren't "healers" because there's nothing to heal, in large part because what healing there is to do is done by tanks who de facto ARE healers at this point and getting worse. I don't mind if tanks help with healing, I very much mind when tanks take over healing. You wanna pop a party shield that saves me GCD heal so I can just use an oGCD? Great, you wanna TBN that idiot with three vulns so I don't have to follow up specifically for him and can just cast an AoE heal? Happy days. Multiple benedictions every 25 seconds? Hell, HALF a benediction on a 25s cooldown? NO.
Further to this point, I don't mind tanks having lots and lots of mitigation, particularly if it's as heavily called upon in high end content as people are claiming. Tanks should be hard to kill but they never be impossible to kill, even at the peak of skill, without a healer. If this requires a rebalancing of tank HP and/or damage from enemies then so be it.
Well I agree that Healers aren't healers because theirs nothing to heal, though what would be fun is actual decision making on healers the problem is both tanks and healers have overbloated kits which lead to things like GCD heals vs Damage GCDs not a choice because you can do both, I also fully agree that theirs a line with how much healing tanks can have I've said many times bloodwhetting is a awful cooldown that invalidates healers, warrior also just has a ridiculous amount of sustain beyond that, other tanks are partly guilty of this PLD/GNB but in their case we can effectively nerf mitigation value and sustain value without taking stuff from it's kit, while warrior's defensives/self healing need drastic changes. (I'd argue DRK's in a good spot for self healing).
Tanks being mitigation bots instead of more support oriented is the whole reason why you never heal tanks not because of tank sustain alone, both play a part in making tanks feel more strong I would reduce both and add for tanks to do more then just hold aggro, press your massive mitigation cooldown and healing buttons, I would honestly say current tank design is just miserable and dull for any tank player.
Here's the thing enmity is literally managed by one button that has no effort it's almost parallel to how healers basically don't heal but if not more so.
While I don't think tanks should replace healers tanks helping healers do their jobs effectively isn't a bad thing, that being said the way its currently handled is just horrid for both tanks and healers I think the system needs a massive overhaul rather then just removing sustain or mitigation it's really not a simple task of fixing this mess of a trinity system.
So we shouldn't actually try to fix the core fundamental issues and just remove sustain so you still never actually heal much because the outgoing damage is still too low?
You do realise just removing sustain (other then making tanks more miserable then they already are to play) will just lead to a Band-Aid fix where healers maybe more needed for ultimate's but wouldn't entirely be anymore fun, it's a really low bar for me to just advocate for removing tank sustain and ignoring the problem.
Maybe you'd be content with healers going from never needing to heal, to placing one ogcd heal on the tank extra, personally I want better for both tanks and healers.