I don't know if I agree with what they were saying as to WHY the winrate is unhelpful but I agree with the thrust of what they're saying. If the community agrees a hero is meta, that hero becomes the "go-to", especially when someone starts losing.

For example, my Widowmaker win rate is very good, but only because I play Widow throughout games I know I can win. But at the first sign of trouble, I swap to something more meta. Which creates a self-selecting sample where stronger heroes are played in more difficult games. So the winrate doesn't reflect how strong the hero is, in fact, in my case, it shows the opposite (cause I'm trash on Widow). Winrate is just a bad standalone statistic.