I don't think he's the greatest athlete ever, but he IS an athlete, and he is high on my list. Maybe not top 5, but he's up there. The guy, just looking at this ONE olympics, has 6 gold medals in 6 events, and 6 world records. He can't do any more than that.
Just like in MLB you can only beat the team you're playing that day...he can only win the events he's entered in. And he's done that, and done it in dominating fashion.