Rennaisance is one large quantitative trading firm, there are other bigger and more successful ones however. I happen to work for another very large and successful quant trading firm.
However the Virtu Financials, the Citadels, etc, will always exist, and will be doing exceptionally well whether people realize it or not.
The issue is that these business are capital limited, so you can't reinvest your massive returns to compound them.