Some would point out that this is already happening with algobot hedge funds; the best are very consistently better at short-term trading than any human. Obviously due to the legal system the owners of the "AI" are the ones who have the money.
Long term trading is another matter.
I think the trick is figuring out how to trade alongside them and not against them. Just bring me and my little lots along for the ride please Mr. A.I. Bot...