He said this:
I guess what he means is that since the game used to be more based around teamwork, casuals (which generally don’t coordinate that much) had less impact on the overcome of the match and that was not psychologically good for these players trying to reduce stress playing video games, teamwork build more of a good hype for the competitive scene like OWL.
But the other problem I see, that he didn’t mention obviously, is that the most individually capable heroes, like those good for solo queue, such as Hanzo, Sigma, Orisa, Baptiste, Moira, these generalists and multitasker heroes, are the ones proving to provide the most value making teamwork reliant heroes obsolete in comparison.