Except nobody is focusing exclusively on that at all. It is one of many problems, as many of us have repeatedly said. The fact that there are other problems that make healing boring does not mean that tank self-sustain in its current form is not also a problem.
How is the current absurd self-healing "literally the only thing that makes you feel like the resilient chonkers you are supposed to be?" I thought your higher defense stats and your defensive cooldowns took care of that. I mean, my secondary job is GNB, and I can safely say that I am not leaning on Aurora or the Heart of Corundum excog to feel like a "resilient chonker." Rampart and Grand Nebula do that job just fine.
Why? Tanks were plenty resilient before they started taking over the healer role. Was GNB the squishiest squish that ever squished back in ShB, because it didn't have an excog stapled to Heart of Stone or a second charge of Aurora? Doubtful.
My point is that unlimited self-healing has never defined the tank role in this game. You aren't "losing" anything except being overpowered. You seemingly demand that you be made OP in some other way to compensate for no longer being able to solo current content. You should understand why this is unreasonable.
Tank self-sustain needs to be limited, not removed entirely. It should be able to make up for a blown heal, to buy time for maybe 30 seconds if a healer goes down. It should not be able to let a tank waste 15 minutes of the party's time by slowly soloing down a dungeon boss.
And in any case, You. Already. Have. Defensive. Cooldowns. To. Be. Tanky. You do not need infinite self-sustain in order to be tanky.
That is what tanks already were prior to EW, so, uh, yes? The healer's primary job in every MMO has been to heal the tank, because the healer's job is to heal damage and the tank's job is to take damage. That is kind of how trinity MMOs work.