http://postimage.org/image/glqgofyf9/
If you felt his damage was lacking, you weren't positioning his shadows correctly to do damage. During team fights it's so simple to have them surrounded by your 3 shadows, and if they all hit their the same target(s), you regain energy. I'm pretty sure once people learn to use his shadows well, he'll be a ban in ranked cause of his insane kill potential, not just because people don't know how to counter him.
EDIT - His shadow cooldown goes lower every time you hit your E skill (the spin), and it gets reduced even more if your shadow hits too.