This was exactly my conclusion today after I did some research about Numerai.

At first I thought: what a great idea!

But after I've jumped deeper into details and read the whitepaper, my question is this: what's the benefit of doing it on the blockchain?

Numerai depends on a central entity that runs the underlying hedge fund and pays the rewards. The only benefit I can see is in this case is the convenience of issuing a currency. But it's just a matter of convenience, not necessity. The whole thing could just as well be based on a centralized scoring system.