Hard to say. In retrospect, I think it is certain he would have been a very high draft pick had he finished HS and gone that route. So from a draft status, there was very little upside in going to USC.
Also, when he got to USC, he was very young and some of his weaknesses were exposed in a way that might not have occurred if he was being developed in the minor leagues.
As for whether he should have tried to keep catching - another hard call. With a rare arm that he had, it probably makes sense to pitch. But it seems like a 95 mph arm is not as rare now as it was even in 2008. A left handed batting catcher with a big arm is pretty rare still.
I don't think, however, that there were ten California HS catchers better rated than him at the time. I saw him as a sophomore in HS and he was very impressive.