Quote from Nattdog:
they are different funds with different strategies.
Medallion is a short term quantitative futures fund. This is the fund with the legendary performance that no longer has outside investors.
RIEF is a more conventional long/short equity hedge fund that uses models more similar to what other quant equity funds use.
RIFF is a futures fund but is longer term in nature.
They have different mandates and different strategies and consequently different performance.
Medallion has been so good that sharing returns with investors on a strategy with size constraints is just giving money away. The other funds that by mandate do not have a chance of being stellar they would rather collect fees on.