actually he's very good on the PP. Yes, he has "difficulty" hitting the net, but name me another guy we have that can move laterally & spread the penalty kill box like he does. Martin can't do this, Despres has the skill set, but isn't ready to QB a PP, etc. Sarge was also very good at doing this. When you start creating movement up high, that opens things up down low where Mr. Crosby tends to make his living. Plus, Letang hasn't played in a week or so, so his timing will be a little off.
He's very good at aspects of the PP. He's terrible at others. Namely, shooting, decision-making, and, sometimes, simple passes. This doesn't combine to make him "very good on the PP."