Put links to the actual stats at the end.
Agree with your overall observation as think that every QB follows their own development path. Additionally its necessary to look at the supporting cast and coaching.
In Quinn's case: saw his career as three parts: rookie (as mentioned in the thread), more knowledgeable but could not hit receivers in stride the longer the pass the worse the problem, and then a new coach and scheme ... besides assembling a better receiver corps Weiss changed to more passes to a "hooked up" receiver - his jr and sr years with pretty similar but had vastly superior stats vs fr and so years. As a Browns fan had serious doubts about the NFL as he often held onto the ball too long and floated passes his receivers got to faster than defenders. Sadly he was unexpectedly injury prone so to me the jury is out on what kind of a NFL QB he would have been.
BW and BQ did have statistically similar years as a first year starter - actually a bit of a surprise as BQ had a lot more career game time before that. Hopefully BW will make a leap like Brady made in year 2 - if so think it will be the result of way better mechanics and the coaches developing a more effective receiving corps and a scheme that results in more completed long passes. The other concern for me is getting an effective running game given the lack of numbers and loss of talent - do not want to have to throw to win.
BQ: https://www.sports-reference.com/cfb/players/brady-quinn-1.html
BW: https://www.sports-reference.com/cfb/players/brandon-wimbush-1.html