It’s also the easiest if you want to make your own “distro”.

A “distro” is ultimately just a prebuilt configuration.nix file. NixOS itself even has tools to provide ISOs and QEMU images based on the build.

I've been thinking for years now that most distros could be replaced by a system config for NixOS or Guix System. I wonder if we'll ever see things go in that direction.