By geometry, both bikes are outdated compared to newer bikes with modern progressive geo like the 27.5 Ibis Mojo or Transition Scout.
Both bikes have outdated drivetrains except that you upgraded the Stance. I would want 1×12 wide-range Shimano or Sram drivetrain.
Both bikes are mostly budget builds. The stock Stumpjumper is a little bit better but not by much.
Then you have to consider how much wear and tear the Stumpjumper has. In the end, I don’t think you would gain much with the Stumpjumper and I don’t think that the Stumpjumper is worth much because it is mostly outdated. Bikes not only wear out over time but they also become outdated. If the Stance is not worth upgrading then neither is the Stumpjumper.
In general, I don’t think it’s worth upgrading most bikes. Buy the best bike that you can, ride it til it’s beat, save your money, sell the beat bike, and then buy your next best bike. In the end, I think you would do better by buying a new budget ~$2000 bike. Here are some I like.
Vitus Mythique 29
YT Jeffsy 29
Giant Trance 29
Commencal Meta TR 29
With these bikes you get the better geometry and drivetrains.