We'll never truly know the answer to that. If EJ hit's most of the open receivers in that Houston game, Hackett wouldn't get a mention as the Bills would have scored 20 something points. Even though the run to pass ratio was off, I had no issues with most of the play calling. The receivers were open, it was just poor execution by EJ. So, I wouldn't say EJ was limited, but I bet some plays were called over others because of his struggles...
As for Brown, "put the other guy in" is always the solution to an ongoing problem. I do like Brown, but I think Spiller and Jackson are a great 1/2 punch. The only thing that concerns me about CJ is the lack of a contract, could be why he's heading to sideline so often. I hope not, but it has to be in the back of his mind. Anyway, I think a competent QB will open up the run game, is KO good enough to do that is the question. I think he can be.