There are several I can think of that were great in college, and crap in the pros, and vice versa.
But you are using an example of someone that professional scouts saw as a sixth rounder, not impressing you are much as whoever... So... Did you know he was a hall of fame quarter back then? Does that mean Jones might be a fifth rounder?... That's the flaw in your example and logic. Peyton, Newton, Marino, Luck, if he had impressed more than them... That's a big deal. (Newton is average, but in COLLEGE, which is when you saw Brady, he fucking dominated).
Anyway, I would explain it more / better, but it's Monday.