Kirk Cousins hasn't broken 9 wins with equally talented teams. The Redskins have also hovered around the Bills points per game the last three years. 2015 the Bills finished 12th in points per game, while the Redskins finished 10th. 2016 the Bills 10th, and the Redskins 12th. 2017 was the biggest gap, the Redskins finished 16th while the Bills finished 22th.
Cousins might put up pretty numbers, but the Redskins have struggled to win games with him.