I have all of my config in a flake, but I think both are fine. Not everyone will use Nix the same way. And it’s easy to see a progression path from using Nix with package installation from nix-env, to flakes, to NixOS. Some people might stop along that journey, but Nix might not have been a good fit for their usecase then anyways. It’s already way too hard to break into the ecosystem, no reason to make it harder.