A neat boost to DRK's DPS and a good way to make it more engaging and reward more skilled play is to A: Put DP back where it was and B: have Dark Arts reduce the recast time on Carve and DP by like 2s or something per cast. In this way you have more frequent checks to see if you're managing your mana properly, because DP and Carve will be coming up more frequently and if you lack the MP to use them because you've been DAing a little too much you can't use them/Dark Arts them. In this way you reward skilled play with higher DPS while punishing less skilled play with lower DPS.

We could also do this with Shadow Wall, where every cast of DA reduces its recast time by 5s. This would go a long way towards giving it parity with Vengeance as well.