I don't recall hearing about a high school senior who could have gone straight to the NFL before Clowney. That messes with your mindset, knowing that you have to stick around for three years when plenty of people are saying you're capable of going right away. I don't think we've seen the real Clowney.
I think you have to look to basketball for comparisons. Is Clowney like OJ Mayo, or is he like Kevin Durant? Or is he like Kwame Brown or Jonathan Bender?