Anybody that says he's only had one bad game (Oklahoma) has only watched him in one game. The reality is the Sugar Bowl was his worst game, but he wasn't a dominant player all season. He looked terrible his last 2 games against Auburn and Oklahoma.
You're not ready for the NFL when you look like that. Kouandjio has the talent, but he was helped tremendously by playing next to Chance Warmack. A lot of his struggles this year are due to playing next to his younger brother Arie, who has been a liability in pass protection. But he's still not a dominant player.
I know what Chris Samuels and Andre Smith looked like at left tackle for Bama. They were dominant players. Even an out of shape and unmotivated Andre Smith is an above average starter in the NFL. Koundjio needed to stay.