Aren't they effectively acting as a prop firm for the contest winners who get to trade $100k capital and keep 100% of the profits ?
Not really. The contest is a way to attract lots of candidate managers for the Q crowd-sourced hedge fund, which, as best I can tell, is the heart of their (likely revised) business plan. The fact that there are monthly winners is just marketing material. The real prize is if Q succeeds, they can fund algos up to $25M with institutional money. And to get to their goal of $10B, my sense is that some Q quants could end up with $100M or more. Or the whole idea could go up in flames, which is what most good start-ups should end up doing anyway, if they have the risk-reward formulated correctly.