Dak Prescott over the last three weeks has played the best football I've seen out of him, probably in his entire career and I give him an easy A for this season.
All that said though the top 10 list provided includes a 7th round pick, a 4th round pick, a 2nd round pick, a guy that no one really wanted when the Rams dumped him, a guy who entered the year as a backup, a guy who was awful until Tyreek Hill came to town.
Not saying you move on from Dak, not saying that at all, but I will say that you can't be afraid to move on from a QB. In the NFL today unless your name is Mahomes (and probably with Andy Reid attached) I think it has so much more to do with how established your roster is as much as anything. Purdy on most other teams probably never gets a chance, but in SF where Jimmy G made a superbowl hes #2 in QBR.
My hope is Dak take the Cowboys to the superbowl and forces Jerry to pay him whatever he asks this offseason Joe Flacco style, but if we get another December/January let down I still think you keep all options on the table as you think about the best way to build the team to a championship level.