My issue with Quick, and all our receivers for that matter, is that they don't attack the ball.
You're taught it since Pop Warner (at least I was.) If the ball is in the air, it is yours, so go get it. Its like they wait for it to fall into their hands and if it is slightly overthrown, there is no effort to try and get it.
Pettis occasionally attacks the ball, and that's probably why he is our most dependable receiver.