throwing knives precision HITS reset the melee cooldown. That'd definitely be worth the exotic slot and leaves a perk to be used. Maybe as an extra effect, blinds the enemy too? That'd probably be too OP though. Edit: For balance, you can say "hits, not kills, reset the cooldown". That way you can use both the exotic and the perk. Or you can use the exotic and kill the thralls, acolytes and dregs the old fashioned way. Leave the knives for the real baddies.