Easily Mahomes and Jackson. Jackson because his runs and buying time are natural, you don't have to see him think about the next step.
Watson and Jimmy G would probably yield better results here since they're better/more fluid passers.
Cam, Bridgewater, Carr I would say would do very similar to what Dak is doing here.
Murray seems to have progressed a lot compared to his bum rookie season and may soon take a spot above.
Burrow is definitely on pace to take a spot over Dak in the coming years.
I left off Wentz because "always injured", but I'd place him in the slightly above Dak tier due to his natural ability as a passer.
This puts Dak in the 5-8 range of QBs younger than 30. After 1-2 seasons there's a chance he goes to 7-10. I don't see Cam, Bridge, or Carr getting any better and that's how I feel about Dak at this point. 5th season, he is what he is.