Obviously, DRK has some problems. A lack of physical damage reduction outside of TBN and a boring rotation are just two of those problems, and I feel that the best way to address these problems while maintaining DRK's status as a "Shield Tank" is by leaning into TBN and it's uses.
How would that work, you may ask? The answer is simple: Enhanced TBN, Oblation becomes a small shield with a lower CD.
Oblation: Shield of 15% health (TBN style) with 2 charges, 1000 MP cost. Restores 500 MP if not broken, and grants one Dark Arts if broken. Can be used on other players.
Enhanced TBN: Big changes, with the inclusion of a 1500 MP restoration if not broken and adding two charges of Dark Arts if broken. Cannot be used on other players.
Dark Arts charges can now be stacked. (Maximum of Three Charges)
I feel that these two changes would still encourage a similar playstyle with TBN across defensives, rewarding knowledge of fights with extra DPS, while providing an ability which maintains some momentum outside of TBN uses. These changes would also provide some recourse if shields are not broken, instead of simply punishing the player. This would also mean more actively pressing abilities outside of the 123 combo and BW / Delirium pop.
Tldr: Mini TBN, Buffed TBN, Half MP refund.