I don't know what do all theses peoples have with "Dark Art not fading on execution".

The sole point of the skill is to have a charge system transfering MP into raw potency, making it a buff with a duration would just create a breakpoint where you try to weave 3 weapon skills and 1 to two ogcd into a DA window, and making it's MP cost completely bursted for high ping users, and worthless for low ping users.