Precisely why asking for more buffs is an issue for Dark Knight, is because of TBN. TBN maybe trash in Dungeons, as I repeat again, high content this ability is super powerful and strong barriers is a dominant force for mitigation, vs reduction mitigation. TBN alone can soak a tank buster by it's self, specially now Oblation exist. Removing TBN, Oblation obtaining buffs, Dark Mind changed to all reduction to counter part HoC/NF/Intervention would actually solve one of the problems in balancing.
No TBN
Oblation 15% Reduction, 250 Potency Regen, 2 charges, 8 seconds Duration, 12s Regen, 60 seconds cooldown, can use on anyone.
Dark Mind 15% Reduction (Physical/Magic), 15 seconds duration, 90s cooldown.
Can at least survive all content than specifics, maybe a clone sadly since I can't come up with much, Barriers are a dangerous game.