Maybe consider not putting more blood on our abilities? We already have a steady gain every 30s as is, so I don't think it'd be a good idea to focus so much on resources even when trying to change DRK's kit. While yes, DRK needs sustain, it needs a proper sustain - not something you just slap on there like WAR does with Bloodwhetting and just straight up self-Benediction(which is still pretty broken imo). The other idea for TBN granting half MP cost would screw up our MP economy quite a bit, esp. since we tend to hold our DA Edge for burst or when we put our next TBN up last time I checked since it's a 3000 MP pay ahead. Halving the MP is basically the same effect but worse.
Your version of Dark Mind causes issues for Shield Healers in particular who mitigate the damage thinking this way. If you use Dark Mind when a Tank Buster is coming up and it's Physical, OOPS! I got rid of my shield and now I'm dead because I didn't have enough mitigation to cover it. I would prefer that we don't push them in that direction and instead just replace Dark Mind with something that works in tandem with DRK's kit in general since it's an archaic relic of HW. DRK just needs a 3rd generalized mitigation to apply to itself to match the other tanks and it'll feel better in terms of survivability(sans sustain, which we'll get to in a second).
I've been trying to wrap my head around how to deal with DRK's dilemma given how much of an issue it is just to stay alive during pulls(TBN cracks in large pulls VERY QUICKLY). AD has a stupid cooldown and is tied to C&S, so it's unreliable except for burst heal situations on 5+, and to top it off the only attack that actually heals you is Souleater(it's garbage). In general: Why don't we just bake in healing to the AoE combo? Not as a trait, just in general. It'd make DRK's survivability far greater in dungeons, since in ST DRK doesn't have as hard a time outside of needing a heal here or there that the healer can provide. If it's not enough, then simply just follow what the other tanks are doing: Give Oblation a Regen effect. All Tanks generally get their regen/recovery effect at 82 or so, so let DRK follow that path too. It may be "homogenization", but DRK desperately needs it to be able to operate without requiring the skill floor it already has when playing the job.