I think Russell is a losing player now. He's still capable of putting up good stats, but his style is heavily dependent on big plays. He could offset that dependence in the past by extending drives/plays with his legs, but he's no longer capable of doing that consistently. So, as Throwdown's attachment notes, he has multiple drives with zero productivity. Those are not obvious on his stat sheet or highlight reel, but their impact is dramatic: It's difficult to win games when your offense struggles to do anything for two straight quarters. It's even more difficult when your QB is turning the ball over.
Part of this is the shift in how the NFL is played. If this were the early 2000s, Russ would still be an elite QB. But winning in today's NFL is more about efficiency and consistency. Russell's style lends itself to the opposite.