You're wrong with your rankings.
The 5 games Kellen started in, the team averaged 21.4 points per game (wining scores of 20,23,25,22 and a losing score of 17).
The NE Patriots averaged 21.4 points per game this year and were ranked 17th in scoring. The Falcons and Giants were tied at 21.5 points per game for 15th and 16th place.
Dak averaged 28.8 per game in games he started, including the playoffs.
The Cowboys as a team ranked 4th at 27.5 points per game.
Rush was middle of the pack, not great, but also not near the bottom.