Not sure this is a good example. Would guess he went there to play for Saban (he is the premier DB coach in football). Saban isn't there any longer, so why stay, especially if he can get paid AGAIN to go play somewhere else?
I think there are better examples of kids that have left and didn't benefit from the move than Amos. Specifically Errol Rogers is the first that comes to mind, but he wasn't the impact player that Amos was.
I think Emani Bailey was hurt the most, as he would've been the #1 back at UL versus what he has done at TCU. However, I think Bailey's decision was driven a lot by getting back close to family and playing with his brother. It just happened that TCU didn't offer him out of HS or we would've never gotten him.