I think the biggest aspect of USC QB syndrome you are forgetting is incredible talent... on the team around them. Big name, high profile college teams get the best recruits which lead to physically talented QBs playing with the best O-lines and WRs; and in the college level athleticism dominates. They do well, their coaches hide their weaknesses, their egos explode from being the hottest ***** on campus.
Then they get to the NFL where the talent gap is much, much smaller. The windows to throw into are smaller combined with having much less time in the pocket. I think NFL game speed, parity, and playbook complexity are too much to handle for these QBs who arent used to nor willing to put in the time.This is common problem with many QBs coming from high profile teams, there are exceptions of course, unfortunately USC has very few of those exceptions.
