But they’re roughly the same paradigm as docker, right? My understanding of the Nix approach is that it’s still reproducing most of a user land/filesystem in a captive/separate/sandbox environment. Like, docker is using namespaces for more stuff, Nix has a heavier emphasis on reproducibility/determinism, but … they’re both still throwing in the towel on deploying directly on the underlying OS’s userland (unless you go all the way to nixOS) and shipping what amounts to a filesystem in a box, no?

I daily drive NixOS. I don't have a global "userland". Packages are shipped from upstream and pull in the dependencies they need to function.

That means unlike Gentoo, I've never dealt with a "slot conflict" where two packages want conflicting dependencies. And unlike Ubuntu, I have new versions of everything.

Pick 2: share dependencies, be on the bleeding edge, or waste your time resolving conflicts.