I'd love to see a definitive analysis, but the ones I've seen indicate that both these things are true, but that most of the problems stemming from Brady's schemes and play calling. As many here have observed, he's predictable, limited, slow to adapt, late getting plays in, has not adapted his offense to the receivers he has, and lacks innovation, creativity, and vision. In short, he's just not a good coordinator. I'm encouraged that McDermott fired Dorsey, so maybe he will pull the trigger on this guy.
Who would replace him, though? I really doubt he would bring back Daboll. Kromer might be the answer. He was terrific his first year with the Bears, setting franchise records for yards and touchdowns. I don't see how he could be worse than Brady.