Book smarts doesn't equal football smarts.
I have two degrees over Cum Lade, member of two honor societies and taught for more than a decade before my current job. Doesn't mean I can effectively run a football team. As much as I criticize Garrett I doubt I could do it as well as he can, and he sucks.
No doubt Garrett's smart. Might be too smart for his own good honestly. The over analytical brain can lack good instinct in the right circumstance.