I think this is about right.

Nix feels pretty close to "right thing to do", but if the other solutions are more successful, it's a case of "worse is better".

I think the important part is usability compared to what's already there. It's much easier to write a Dockerfile than to write something with Nix. You can get much stronger benefits from Nix than from a Dockerfile.. but, most of which you don't really need all the time.

My impression is the other solutions are quick-ish hacks to solve problems that come from (and building upon) the complexities of systems built using quick-ish hacks. Nix feels like a more elegant solution, but it's also different enough that it's got a steep learning curve for anything harder than "install foo".