The thought (among some) is that Cooper Rush is better than Dak and the belief is that Dak struggles when the opposing defense shuts down the run. So, let's see what Cooper Rush is able to do it an opposing defense is able to shut down or limit our run game. And as you say let's see if Cooper Rush has the ability to rally the offense or keep the Cowboys in games when the defense isn't having such a great day.
The difference in games where the team fell behind multiple scores with Dak as the QB and games with Cooper Rush. When the offense went through multiple drives or a period of time in which they couldn't score or move the ball much. Is the defense with as the Dak QB, wasn't able to limit and shut down the opposing offense while our offense was in a lull. So the Cowboys fell behind multiple score and Dak had to attempt to rally the offense back. Thankfully the defense in this last two games were able to shut down the opposing offenses, while our offense was in a lull. So we have yet to see what Cooper Rush is able to do if the defense can't do what it did during the last 2 games and Rush is in a position where he has to rally the team from behind or he has to match the opposing offense TD for TD, if they score 30+ points.
Here is a hypothetical:
The cowboys have the top defense, special teams, and run game
1. Tom brady is the qb in his prime
2. Dak is qb playing at his highest level
Tom Brady can win you a superbowl, and Dak cab win you a superbow. Both would be completely adequate to get you where you want to go.
THe cowboys hypothetical scenario:
The cowboys have a very good defense, special teams, and running game
1. With the additions of Gallup, Cooper starts throwing in the 300+ range, continues to not turn the ball over, and keeps winning games
2. Dak comes back, but has some lingering issues, takes time to knock off the rust in his game and get over injury
Both can get you into the playoffs. One is showing and known, the other is a what if. That is where the controversy would be. Do you stop what is working and hope an unknown will work
I personally think dak will come back and play great, but I am rooting for rush to start having those big time games and keep the job, because it is the known or what we are seeing