The fact is that many (hundreds) do beat benchmark - over years and decades - which is sufficient data to disprove the original assertion that I was contesting.

The fact is that many (hundreds) do beat benchmark - over years and decades - which is sufficient data to disprove the original assertion that I was contesting. "By how much?" - not relevant to the claim I was disputing. The reasons there are many outperformers are few fold. Firstly, failing funds often close up shop and start anew, which artificially inflates the N success metric. The average number of hedge funds that a current manager has run is 2, since they've closed one failure on average. Second, economic theory is a limiting condition, it's still remarkably easy to be lucky over a 5 year period given the low frequency nature of trades that many of these funds perform. It's not like a chronic gambler where the law of large numbers kicks in after two weeks. Third, professional fund managers still do have edge over all other parts of the market (this has been shown in academic research), it's just that this edge is less than their fees, but it tilts the small sample statistics towards showing a large N successes compared to what we'd expect if they were trading randomly.