The Definitive Dark Knight Guide

[Malusion]

C&S is only 50 potency more than a DA/SE and does not heal. If you have plenty of MP, go for the extra damage; but to say if you aren't managing your MP if need to use C&S for mana is incorrect. By using Blood Price and C&S for MP, you are able to keep alternating Delirium and DA/SE combos much longer. This is more DPS and more incoming healing. It seems that you are just happy to see big numbers when C&S crits.

You have to count how much potency increases with DA, not the total. Dark Arts adds 350 potency to C&S, and 140 to SE. Trying to count the potency before DA that they do as part of the amount gained doesn't really work.

Edit: As a side note just to echo your other point, Blood Price mana gained is indeed not based on damage taken, it gives a flat amount of MP back per hit regardless of how much the hit is for.