I wish people would stop spreading blatantly untrue things about TBN and how it's "So good because it stacks with mits". You need actually useful mits for TBN to function as well as we pretend.
The math part 1 | 2 | 3 | 4 | 5 | And a bonus to show this has persisted since EW launch.
If you don't want to read all of that, here's a tl;dr: DRK mitigations are among the worst and TBN does not make up for it even in a perfect and ideal scenario of purely magic damage. The idea that TBN is any good holds the class back from actually having decent defensive tools even when facing magic damage since the amount of raw damage they take is significantly higher than the other tanks. TBN is bad and we need to get off the copium. The math is there. TBN is not the problem, but it needs to stop being used as a crutch to its design. I'd rather see TBN removed and given actual mitigation tools than see people keep blowing its usefulness out of porportion. If you go in a dungeon as a DRK you are going in disadvantaged from the beginning.