Another reason why I lean more towards the older guys instead of the highly rated recruits who dropped, I believe in early and late bloomers. If you were at the top of your class and lost ground, I think it's much more likely that you were a late bloomer. OTOH, if you made massive improvements through college there's a better chance you're a late bloomer.
Besides GG, I think Dariq Whitehead is another example of this principle. I don't see him as a high potential prospect despite coming in as the number one recruit. I do like him more than GG, however, because he has a better body of work to suggest he can be a role player. If GG had more role player potential I wouldn't mind drafting him, but his defense, physical tools, and attitude leave a lot to be desired.