The four-year starters seem to be late bloomers or guys who go to poor programs or guys in the right place / right time. I'd rather have a Manning or a Luck but those guys don't grow on trees..
Typically, the more college starts the guys have, the more likely the scouts are correct about their evaluation - when you have a guy like Matt Ryan who started 35+ games in college, the error bars are relatively small. If the scouts say he's top of the first round, he's probably going to be able to start at the NFL level - if the scouts say he's a 3rd or 4th round pick, he's probably not going to be able to.
The problem with Trubisky is that they have almost no data on him - which means he's super risky, so unless his ceiling is ridiculously high, you shouldn't be thinking about him that early. The fact that he has very little data because he couldn't beat out a guy who wasn't a pro prospect is a definite knock - this isn't Matt Leinart who was sitting behind Carson Palmer.
Manning was a 4 year starter, and Luck started 38 games.
Winston started 27 games, and was redshirted as a freshman behind EJ Manuel, who was drafted in the first round. Being blocked by a senior who gets drafted in the first round isn't remotely comparable to being blocked by a guy who doesn't get drafted.
Rodgers started 25 games at Cal, was the starter the second he showed up at juco, and the starter the second CAL grabbed him. Rodgers ended up at a juco because he didn't look the part (he was 5'10 as a highschool senior)
Newton is probably the closest - but he's not actually close because the reason for the low starts was never talent. As a freshman at Florida, he was blocked by a senior who was drafted in the first round(tebow), then got arrested, and transferred to juco because he was going to get expelled. He was the starter immediately there, played a year, and then was the starter immediately at Auburn.
I can't come up with any positive comparables that weren't good enough to start until their senior year, and then got drafted high and became NFL starters.