Case in point: the first algorithm on this list [1] of community contributed algorithms that were migrated to their new platform is "minimum variance w/ constraint" [2]. Said algorithm showed returns of over 200% as compared with 77% returns from the SPY S&P 500 ETF over the same period, ceteris paribus. In the 69 replies, there are modifications by community members and the original author that exceed 300%.
Working together on open algorithms has positive returns that may exceed advantages of closed algorithmic development without peer review.
[1] https://www.quantopian.com/posts/community-algorithms-migrat...
[2] https://www.quantopian.com/posts/56b6021b3f3b36b519000924