He sounds like Wiz Khalifa, so how bad he is depends on how much you like Wiz. I think Wiz is just bleh, so I’m not in love with Mac Miller. But he’s actually a bit better than Wiz, and he’s white, so obviously he’s going to get attention.
Is he better than Asher Roth? Technically, perhaps. Stylistically, no. Their styles are definitely different though.