Medallion has about $6.4 billion in assets and they have kept it about that size for quite a time for a reason. It would be much harder to get those high returns when trying to invest $100 billion like Buffet tries to do.
Based on what I see from quant prop trader friends of mine in the Chicago area, if Medallion was an order of magnitude smaller they could probably juice their returns up to 150-300% pretty reliably.