Most of this is historically inaccurate. You didn't take DRK into raid in HW because of mitigation. You took it because WAR/DRK offered higher raid dps than WAR/PLD or DRK/PLD. You'd still generally take it into a fight where DRK was at a mitigation disadvantage (i.e. any physical fight), as long as you could compensate with smart use of defensive cooldowns, because it offered higher raid dps than PLD. The exception was on fights like A7S prog, where PLD's defensive advantages and the fact that LD is a liability in that fight tipped the balance in favour of PLD/WAR.
Now that PLD does more dps than DRK, it's a complete non-issue. DRK has never been the 'default tank', and likely never will be.
TBN is never a simple dps gain or loss. Even in Grit, where it has fairly consistently been a dps gain on average, it's always a dps loss whenever the resultant Bloodspiller replaces Siphon Strike. This is kind of hard to predict without mapping out your GCD usage for the entire fight, so you're really only going to see definite net gains after using it in Grit at least six times. (For example, if the first GCD that you replace is SpS, then TBN is a net loss in Grit on the first, second, and fourth uses, and becomes a consistent gain after. But this also implies that you've either spent 75 seconds in Grit or about 4 DA worth of MP/672 potency on Grit stance swaps. Which is pretty gross.)
You also have to consider the fact that DRK has never had access to Blood Weapon in Grit. It's basically like what would happen if FoF or Berserk were only available out of tank stance, and if tank stance cancelled the buff. If Blood Price is to be the Grit equivalent, it needs to provide something equivalent to BW, both in terms of rate of resource generation and in terms of effect.
The biggest issue is that it's nearly useless in single target. It really needs something along the lines of reducing the damage penalty of tank stance, and/or lifting the MP regen penalty when it's active, in order to ever justify using Delirium on it. Even there, forcing the player to stay in tank stance for 30 seconds just to get the full effect is a pretty tall order.