At the moment there are only 4 Potter attractions, exactly the same as Marvel attractions and that is divided between two parks, so I don't think it is overkill; I don't think the new coaster and the Ministry of Magic will make it overkill either, though I do hope that is it then. Personally, I don't care much about Potter, read some of the books and saw the movies, it's ok, but nothing that special nor original. It makes for a nice theme park experience, and most importantly, the rides are good, that's really all that matters to me.