I agree and disagree with this.
There are some guys, like Ben, Bradford, Ryan, Manning, etc. that are simply NFL ready the day they stop onto the field. Then there are other guys, who are simply not ready right out of college and need a lot of work before they are ready for a number of reasons. One being the coaches they learned from in college and the offense that they played in.
The guys that are NFL ready like Manning, Ryan, Bradford, etc. can get thrown in right away and learn to succeed. The guys that aren't, like Eli or Romo or Rodgers, probably need some time to develop and improve their mechanics and learn the playbook and how to break down coverages. These guys benefit greatly from sitting on the bench and learning from veterans like Warner, or Bledsoe, or Favre and eventually take over good teams with a stable coaching staff and offensive scheme.