Wentz has a tendency to miss easy throws, throws that Goff typically does not miss. Wentz has the ability to make those amazing "How the freak did that happen?" throws that you only see from a few QB's, like Big Ben or Wilson. If Wentz can get those easy throws down, then he'll be a lot better, if he can't then that's going to shorten his career. RG3 could make those throws but he couldn't play from the pocket.
Wentz is better from the pocket than RG3 is, but that's still his weakness, and that's why I wanted Goff. Better in the pocket typically translates to longer times playing at a high level. If Wentz can master the pocket he's going to be a very dangerous QB.