Once again, I feel compelled to mention that the 'solution' to this problem already exists in the game, were SE able to realize it: Swap all Tank HOTs to Self-Barriers. WAR can selfheal itself into the stratosphere at the moment, thanks to Equil/Bloodhwetting/Shake it Off. But, if Equilibrium was changed from 'heal 1200p, plus 300p 5 times' to 'apply a barrier to self for 1200p, plus 5 layers of 300p barrier', it's giving the same amount of EHP yes, but any HP that the WAR loses, they've lost until the Healer heals it back. Same for Bloodwhetting, if the crazy healing is swapped to give a crazy shield (with a 6s ish duration), then they still remain 'invincible' in dungeon pulls, but as soon as that shield wears off, they will need a healer to address the HP they're missing (instead of the current 'drop low, Holmgang, BW as it runs out and restore to full again'). Or for PLD, Holy Sheltron could swap from 1000p total regen, to 4 layers of 250p shield, which ironically would make them MORE tanky (due to having extra up-front mitigation vs a hit, due to that first shield layer)
There's more ways to make a Tank feel like it has good 'self-sustain', than giving them so much healing capability that they take over the Healer's job