DRK - Is it worth using Dark Arts Bloodspiller without Grit?

[Mithron]

From what I understand, since DA+Bloodspiller potency in Grit is the same potency as no Grit, it's usually used in Grit to keep DPS, and outside of Grit if you have excess MP and Blackblood.

So then, only DA Bloodspiller if you're in Grit or have excess MP as off tank? Save DA for Siphon and Souleater?