The only way that Cooper Rush will ever start a game for the Dallas Cowboys is if Dak is injured and physically cannot play.
Cooper had a great five game run. In the first four games he didn't have a single turnover. During those four games, Cooper averaged 193 yards passing. He ran with the ball 9 times for a total of 6 yards. The Cowboys averaged 22 points a game during those four games.
Meanwhile, the defense averaged 14 points allowed per game.
Cooper did everything that was asked of him. He wasn't asked to do the things you would expect of a starter. He was asked to stay within his limited skill set and not make mistakes.
In game #5 against the Eagles, he had to attempt more than what would be expected and we witnessed the reason for the limited expectations.
In the previous four games the Cowboys scored first each time. In that 5th game for Cooper, the Eagles scored first. Cooper's very next pass after the Eagles score was an INT.
The Eagles used the short field to score again. Cooper and the offense followed that up with a four and out. The 4th and 1 failed with an incomplete pass. The Eagles used that short field for a field goal.
Now losing 17-0, Cooper threw another INT on their next drive. For the 3rd consecutive drive, the Eagles started in Cowboys territory and ended with their 4th score of the game, another field goal.
Turpin returned the ensuing kickoff 63 yards, enabling Maher to end the first half with a field goal.
In the first four games the Cowboys defense was able to limit the opponent's scoring, the Cowboys offense needed minimal productivity to win. This is not a criticism of Cooper Rush. Any criticism should go to someone that places expectations on Cooper beyond that of a busdriver with limited productivity.