I'm not entirely sure what the problem is with DRK being similar to SAM, given that the current implementation of the blood gauge is basically a lackluster WAR beast gauge, with Delirium also being basically a non-cd, being only able to burst longer, not higher. Self sustain also does not refer to dps, but to sustaining its own HP. Additionally, the implementation of Dark Arts outlined here is literally exactly the same as it was in HW, which preceded Kaiten lmao, with the only change of being more expensive to offset the removed drain.

Here's the current implementation of Fell Cleave - oops, i mean, Bloodspiller:

Bloodspiller
Delivers an attack with a potency of 400.
Dark Arts Potency: 540
Grit Potency: 475
Dark Arts+Grit Potency: 650
Blood Gauge Cost: 50
Dark Arts fades upon execution.
And...

Fell Cleave
Delivers an attack with a potency of 520.
Can only be executed while under the effect of Deliverance.
Beast Gauge Cost: 50
Current Quietus, also, is just a less powerful Decimate. If Dark Passenger and Quietus being made similar to Shinten and Kyuten is bad, then I'm not sure why the current implementation of Bloodspiller and Quietus aren't a problem with you, given that they are straight up the same as the abilities of another tank. Someone better tell Yoshi-P that Storm's Eye and Jinpu are currently exactly the same as well!

The only part of this that makes sense is what you said about TBN, which is prob true, i'll edit that. Only getting that tool at 70 is kinda ridiculous tho tbh.