imho the whole "let him develop on the bench" or "throw him to the wolves" argument is ultimately meaningless because I believe if you're good enough to play in the NFL, it doesn't matter. Either you got it or you don't, and 3 years on the bench or baptism by fire won't help or hurt you either way.
There may be some cases where one or the other did a small bit of damage. Troy Aikman probably could have used a year or two on the bench, but in the end his traumatic rookie year meant nothing. Same with Steve Young. On the other hand, guys like Aaron Rodgers who had to wait probably could have started from Day 1 and had no problem developing into a great QB.
If you're a good QB and you have what it takes, you're going to make it in the NFL either way. If you flat out suck, all the development in the world doesn't mean jack for you.