It's suggestions like this that are why complexity is being eroded from the game. If that's what everyone wants, it's fine, I'm just pointing it out.
If TBN doesn't break then it's not worth using in that situation again. If the incoming damage is barely enough to take 25% of your health bar, then it's not even denting you enough to make a healer concerned enough to heal. This was the logic I used in Shadowbringers when I mained DRK and it worked fine. I revisited this whenever my gear upgraded and over time stopped using TBN in situations it had stopped breaking in.
I agree that one of the main problems with TBN is that it is not as versatile as the other tank mitigations became in Endwalker. Every other one contains a mixture of raw mitigation, heals and regens. Individually, these things are not useful in certain situations, but together, they are almost always useful for something. TBN is just a shield, so if it is not useful for something, then it's useless.Third, there should be added mitigation to TBN itself. For this I would combine TBN and Dark Mind or Oblation. This would help get rid of button bloat in the job and make it a lot easier to mitigate during a 2 minute burst window.
TBN is useful even against the dots in the latest raids, but technically it doesn't reduce the potency of those dots so once it's gone, you have nothing to save you unless a party member, such as a healer, cares. Whereas I can just about survive longer than a DRK because of the regen that PLDs have.
You have to weave even more to reduce the potency of the dot, which is not necessarily a problem but DRK has a lot of abilities to press for attacks as well. To be fair, other tanks run into this problem a bit because if you combine two mitigations for a tank buster (which I would recommend in Abyssos), it's easy for the timing to fall right when you also need to weave an attack. Easy to time an attack or a mit a bit differently, but easy to get wrong as well.
Overall, any suggestion that involves something other than adding a heal I would find interesting. I like the tanks to be different. Whether Souleater is buffed, a Painhaima effect is added to TBN, raw mitigation is added to TBN or a second shield is available, something other than heals is welcome. Because all the other tanks have that and it would be boring to copy them.