The problem in Stormblood wasn't identity. It was that it was uniquely bad.
DRK had the lowest damage output by a fairly large margin. It wasn't too bad at the start of the expansion when WAR and DRK were about at parity (but well behind PLD), but when WAR was buffed early on, all that changed. DRK was a sustained damage tank at a time when burst was king and had no drawbacks for doing so. Delirium was insipid and weak. Actions were either extremely situational (be sure to Sole Survivor that one rock add that shows up in the entire fight), or locked behind stance (Blood Price and the HP gain from Soul Eater were both Grit only). We were the only tank without a unique AoE mitigation skill at a time when Divine Veil and Shake it Off were being used specifically to cheese Limit Break gauge generation. Shadow Wall was on a 180 second recast at a time when Sentinel was 40% DR and Vengeance was just flat out better.
Heavensward was good, but players were willing to overlook a lot of faults and disadvantages because we could put out some competitive dps at a time tank damage output had a larger impact. Stormblood took a lot of Heavensward's strengths away while leaving behind the drawbacks. Certain expansion-specific issues, like Veil/Shake being obscenely powerful for generating bonus LB (mitigating critical damage generated LB) left DRK consistently warming the bench. Again, that's why I said that context matters. You have to take the job in the context of its expansion in order to understand why it was so bad. And that's why there was overwhelming support for change, both going into 4.3 and later in 5.0.
I think if you look at Shadowbringers as a whole, it does represent a significant improvement over what we previously had. We're still on the lower end of tank damage output and well behind the shield tank, but the overall balance is better than it's ever been. Outside of Living Dead, we're at least not seriously disadvantaged in any one area. And I would much rather take a Delirium that you can meme about than one which is ineffective.
I find it difficult to react to Endwalker's action trailer without having some context on what actions have been removed. I've created a list of the actions that are MIA across all tanks. On DRK, for example, we gain three new actions. We haven't seen any sign yet of Unmend, Shadow Wall, Dark Mind, Living Dead, or Dark Missionary. If I had to play odds, I'm going to guess that Dark Mind is going to be replaced by the new bubble. But what else is missing? Unmend and Shadow Wall are likely still around because Lightning Shot and Nebula showed up in the GNB trailer, but where does that leave us with the last two unaccounted for actions? None of the invulns showed up in the trailer, so if they're gone, tank gameplay is going to be significantly impacted by the change.
There are other questions that I have as well. A lot of players on other tanks have gone on about how powerful TBN is. WAR's new defensive probably replaces Thrill, so is it gaining a TBN-like action? (RPR has its own TBN-like action now which grants AoE lifesteal). Does PLD have a net gain of two single target defensive actions compared to the other tanks, given that they've never really had an analogue to Thrill/DM/Camo? Unless they've lost Sheltron, that's a possibility. Again, without understanding what relative differences will exist between the tanks, it's hard to gauge what the power balance will be.