I often hear suspicion about mise for this reason from people that haven't used it. I suppose it's not surprising. That said, I have spent over a decade in the developer productivity space as well as hundreds if not thousands of hours working on mise in the last 2 years—if there is someone that can build this I'm probably the right guy for the job.
Particularly with dev tools, it's long been the case that mise has solved this problem. Improvements are continuing to be made with things like improving supply chain security and ergonomics with python—though it's not like the python community itself has its DX figured out.
Of course I'm still fixing bugs pretty regularly and that probably won't ever change but there are hundreds of thousands of developers out there using mise (kind of a guess, but I'm pretty sure) and it's working great for them. It's in the top #100 tools in homebrew now: https://formulae.brew.sh/analytics/install-on-request/30d/
This definitely isn't some scrappy project—I've devoted much of my life to this problem and I think all evidence points it it being a resounding success.