Ignoring the fact that a guy at 39 is having to score at almost a goal/game pace to creep up on Gretzky, Ovechkin's health has so much to do with his production.
He missed his "rookie" season due to a lockout. He missed half a season to a second lockout. He lost the equivalent of a season due to COVID, but he has been able to play 77+ games in 14 of 16 82-game seasons. Matthews has played 75 games twice in his career. He's scoring at a better pace than Ovechkin but I have a hard time seeing Matthews' body hold up to playing at this level in his late 30s.