Bolts serves as cast filler that autoweaves if you leave a fraction of a second gap in the rotation, and for when MH eats an input and breaks the incantation loop. In a test setting Daggers Of Daveroth weaved in are a bit better damage, but it feels reaaaaaal bad when MH eats one of the longer CDs and you have to wait it out, which happens over the course of gameplay.

The sig never tested very well, so if youre giving up a basic filler you'd be better off with any of the other incantations before the Eye.