Renaissance is part of the market, and it's the sort of thing that we individual investors can't beat. "The market can't be beat" doesn't mean no one can see better returns - it means a random yahoo like me simply can't compete with the information, processing power, and access funds like Renaissance have.

Thus, an average investor is a lot better off with an index fund instead of trying to pick individual stocks. (Funds like Renaissance's Medallion simply aren't available to people without tens of millions of dollars to throw around, too.)