Cam Newton is the QB. If there's a problem with the passing game, I think you have to begin the discussion with the QB. Of course, every item on the list is relevant. But in my opinion, Cam is the biggest factor.
Though I caveat that with Shula/Rivera not using him properly. Cam is not a true pocket passer - yet. They are literally forcing him to be one and it's gonna take time, and the team will take its lumps in the process in the win/loss column. But it will take that dynamic to win the ultimate prize - Rivera knows that. Cam could win 10+ games this season running as soon as he sees an opening, but good defenses will stop him in the playoffs.
It's just the next step in Cam's progression as a complete QB. Accurately reading defenses pre-snap, and anticipating the throw before WRs are open, particularly in the middle of the field. He's always been confident outside the numbers, which is usually the harder throw, but he hesitates and wants to see a receiver open in the middle of the field before he lets go.
And he has to start completing those deep balls. Not sure what happened, but that was his bread and butter as a rookie. That and the deep outs to #89.