Also new to nixos but the first few hours was a breeze: installed x and i3, commented out, installed waylaid and sway, realised that my configs aren’t ready to switch yet (mainly custom xmodmap) so commented that back out, and i3 back in. I’m still left with a perfectly working system. Such experiments on Ubuntu normally left numerous irreversible changes (granted, mostly through lack of knowledge).

I do see the OP’s points though, people are the weakest point of nix ecosystem, and I wish both projects worked together to solve this, as the tooling/approaches have similarities