I'd currently rate him between 11-15 with the potential to be much better. Show my work? Pfft, that assumes that I care what others think my opinion on him is. I support him and believe in him but he has a lot to work on to improve. It's really hard to rank QB's given that they don't all run the same system. Wins/Losses are a team stat. Completions/Incompletions depend on the receiver and offensive playcalling, etc. Should some QB's be ranked higher or lower based on having a better or worse stable of receivers or much better or worse coaching?
Dak needs to work on his footwork, accuracy, internal clock, ability to read the defense, and qb101 throws (which should be improved by footwork and internal clock improvement). He has good leadership qualities. He listens to his fellow players (like when Amari came in and made suggestions). He's athletic, healthy, can run well and has average accuracy. He works well when when the team is losing to try to make up points, but he usually helps build that deficit in the early quarters. Is he a bus driver or below average? Heck no. He isn't elite yet either (but I believe that the potential is there.) I think his biggest setback was the Atlanta game in '17 that seemed to have wrecked his confidence and clock and it took him nearly a year to recover.
With a healthy O-line to protect him and him working on his weaknesses this off-season and not having to deal with Linehan's poor OCing, I think we'll see a lot of improvement from him.