It took Braxton 3 years to learn all of CFB's nuances and he's still learning. I find it hard to believe Barrett can come in with no exp and just pick up where Brax left off. Its like expecting Bri'Onte Dunn to be Carlos Hyde suddenly, it 'aint happening.
On the flip side, Manziel and Winston both picked up the game swiftly in their redshirt freshman years and won Heismans so it can be done. Barrett was no slouch as a QB recruit either!