I think he was hurt last year by MC not having a very good QB and by Bobby Hall not finding ways to get the ball in his hands other than the wildcat and an occasionally poorly thrown screen pass. And every single time he was in the wildcat, he would just go straight ahead and plunge into the line every single time. Hall could have found more ways to get him the ball like by moving him around, handing the ball off to him on reverses, maybe use him on a WR option, etc. Singleton was much better when Peyton Johnson was the QB because Peyton could throw the ball downfield some and he was a pretty solid high school QB. I hate to bust on a high school kid, but Rowell is just not a very good player. He makes poor throws and he takes too long to make decisions on the option, which usually causes the play to be disrupted.
I do agree with everything that you said about him though- I saw it myself too. He does get frustrated, and I was surprised that he wasn't throw out of the Clinton game along with Giles.
As far as college, Singleton would be a much better fit for Dan's offense. Dan would find ways to get him the ball, and we're going to have good QB's as long as Dan is around. Basically, he would be used like Bumphis with the exception of being used in the wildcat. His speed would be really tough for a LB or safety to try to cover, but Tobias against a CB- he's going to be kind of pedestrian in a pro style offense. Tobias would have to deal with Balis and Dan- and I'm not sure how that would go.