Potter is powerful, but he's also a wuss and relies a lot on his friends and allies, and not that bight, he's only a success because of all the help he gets.
Dresdon is self made for the most part, and only gets advice and help once in a while, but for the most part he does it all himself. (At least in the TV show, sadly I haven't had the chance to read the books.) I know Dresdon has a dark side, but that's all the more reason in my opinion that Dresdon could stomp Potter's ass.