I get what you're saying, but I don't think it violates the Unix philosophy in that way, at least not any more than any other package manager like apt or dnf do

I get what you're saying, but I don't think it violates the Unix philosophy in that way, at least not any more than any other package manager like apt or dnf does. Nix as a package manager is made up of multiple tools that interact, such as nix-env, nix-store, nix-shell, etc. NixOS additionally has nixos-rebuild and other commands that are layered on top of those core Nix commands.