Definitely the coach as always. But the JC years were his years. There's never been any other hype like that. There's never been a team and an offense more blatantly handed off to a QB to do as he wishes than Weis and his prize protege JC, even including an almost slightly bizarre spectacle involving Demetrius Jones' nominal ascent to the starting QB, post Brady Quinn, and the new fangled offense Weis with some fanfare was going to unleash, which lasted approximately three quarters and it was gone. And then not much more inauspiciously could the JC years begin with his first start vs Michigan, featuring an infamous 4-defender tandem sack that I'm sure you can watch on YouTube. And then it was basically downhill from there.
And we did have some elite skill position players. And respectable talent all around, it wasn't some Purdue level roster, that'a a canard of JC apologists. So of course the buck stops with the HC. But I'd be much more inclined to say JC destroyed Weis and not anything resembling the other way around. It was almost like a Shakespearean fall from grace for Weis, dubiously putting all his fortunes in JC's goofy-looking, spoiled rich kid's basket. And then seeing his career suddenly crumble, after getting off to a very bright start, including a huge contract extension. And the rest is history.