Well, just so happen that I did. And it isn't fun. If the healer doesn't follow, I can space out my mitigation as best as a I can, save Abyssal Drain for when i'm at 50% health on big pulls, spam TBN every time it's off cooldown and I will still die.

And you know what ? I aggree, that's kind of how it should be.
Tanks shouldn't be able to basically solo dungeons.
Yet they can, except for Dark Knight.
So either SE rebalances the dungeons to take into account that tanks have high sustain, and give some back to DRK (shorter AD cooldown, bringing back Sole Survivor, maybe with an AoE version etc).
Or they nerf the sustain of other tanks. (Remove the healing on requiescat, remove the 2nd charge of Aurora, lower the HoC excog potency or what have you).

But that's just to even the playing field, it wouldn't make dark knight better in a design sense. Just would it so it doesn't feel like an underpowered tank compared to the others.