For DRK they should do something to his MP managment, someone proposed to allow him using Manadraw, but IMHO is is a lazy and not so effective solution, it need something like:
. enhance Bloodweapon MP regeneration (PvP only)
. While in Bloodprice the your skills require half (or a % reduction) of their MP cost (PvP only)

So you will have to use it mindful and if you do you will have a 20% costant damage buff, that with other side fix (like Sole survivor, carnal chill ...) it makes him a valuable class.