Linux

NixOS likely only refused to run it because you weren't running it in the Nix way. That's not a jab or anything, Nix has a huge learning curve and requires doing a lot differently. You're supposed to use devshells whenever doing development. If you want something to just work, you use a container.

Whatever issue you ran into most likely had nothing to do with NixOS being immutable, and was probably caused by the non standard filesystem hierarchy, which prevents random dynamically linked binaries from running.

I've never heard of flatpak and immutability being obstacles to developers, in fact I generally hear the opposite. Bluefin is primarily targeted at developers, and some apps will only officially support the flatpak distribution, like Bottles, because of the simplicity and benefits it brings over standard distro packaging.

I’ve had NixOS absolutely refuse to run some compiler toolchain I depended upon that should’ve been dead simple on other distros, I’m really hesitant to try anything that tries to be too different anymore.

Yes, some toolchain expect you to run pre-compiled dynamically linked binaries. These won't work on NixOS, you need to either find a way to install the binary from nix and force the toolchain to use it or run patchelf on it somehow.

It would be a problem without distrobox. Since that gives you a normal, mutable OS on top, you don't even notice the immutability.