Keep in mind he is rarely used in his preferred position, that being a forward. He often comes on to replace one of the wingers.
I think if we played him week in week out as a support striker, aka DPs position, he would score a lot more goals and play a lot better. I'm not sure if he'll ever get that chance though as DP, Iaquinta will be first choice for next season as well. Not forgetting we have the likes of Giovinco on loan and we have been rumoured to many other forwards over the past few months.