I completely disagree with your assessment of Hughes' future. First, I don't think he's necessarily destined to be a reliever, but hypothetically, lets say he is going to just be a reliever. Based on what we've seen from him so far, why would you only say he's going to be a middle reliever.? He might not sustain it, but he was nothing short of dominant this year in a short relief role. If Hughes' future is in the bullpen, it's not fair to call him a middle reliever. Instead, set-up man or closer is more accurate.
As for him being a starter, he may, or he may not, but he began to show some promise last May before Wang came back. If he can further develop his change up, in my opinion, there is no reason not to think he can be a successful big league starter.
People love to throw these prospects into groups based on very small sample size. They may or may not pan out, but it has been proven time and time again that patience needs to be shown with them. With Hughes, and also with Chamberlain, I think that patience is important.