> I think it's pretty obvious that the parent is talking about the average investor.

Really? Because this is what the (grand)parent said:

"Whether you're an individual trader or a billionaire hedge fund manager, active strategies lose out to passive ones in the long run."

Clearly grandparent was not talking solely about the average investor.

Yes but it's also a fair point that a lot of actively-managed mutual funds out there don't beat low-cost index funds.