In HW Blood Price was actually pretty decent compared to its SB version now.
It had no restrictions regarding stances, and even vs single target it generated a big chunk of mana.
However the amount of mana it generated was a must because Darkside drained mana over time instead.
Now it just doesn't let you regenerate any mana.
At the beginning of SB, SE wanted tanks to be... well, tanks. They introduced stance dance penality (DRK was not affected), accessories without STR, and locked some "beneficial" abilities behind tank stance, such as Blood Price. But in addition to that, they also nerfed the mana gain from Blood Price.
After a huge sh*tstorm SE removed the penality, and later added STR to accessories, so healers wouldn't get stressed out from tanks using STR accessories. Yet Blood Price didn't recieve any additional changes.
Which is conflicting: if SE wants to loosen the stress on healers, I would image something like small pulls, "full time tank stance"-tanks.
Blood Price is the total opposite: to be effective, you NEED to pull big. But even then the mana generation is not high enough to spam DA Abyssal Drain, neither is the duration long enough to do so.
So, DRK end up pulling big, not using DA AD as much as we would like to, and would rather tank without tank stance. A full load of stress on healer. (In addition, you don't want to DA Dark Passenger, 'cause that would blind your enemies. They hit less -> you generate less mana during Blood Price.)
SE achieved the exact opposite of what they originally intended.
The whole design of DRK is contradictory when you pull big. Their abilities are not complementary. They are counterproductive!
(This was also a problem in HW.)
b@topic: I wouldn't add a "thorn" effect, vengeance already has that, it sound too similar.
I would like it to...
a. increase mana generation (to the point we can get along with mob missing hits)
b. change into a mana "regeneration trigger" with increased duration per hit
c. add a life leech (bloodbath) effect (maybe magical damage dealed only?)
d. usable outside of Grit once again or
e. complete rework