He lacks perhaps Rees best trait - the ability to just perform and not feel pressure. No matter how poorly you treated Rees he'd pop up and do what you ask of him. Even Golsons sophomore year when BK didn't put pressure on him we still had to play Rees in a few situations.
Add to his academic problems and I'm not sure he's tough enough to be an elite QB. He can be a fairly good Qb but at times you need to take pressure off of him. And even in a perfect year you might need a reliever like Rees. Some of its BK but I think Golson wears down more than the average QB