I've been "all in" on NixOS for the past couple of years on my workstations and servers and will say that sometimes you do run into this, but there is an escape hatch. If you really need something that isn't available, you can just create your own package. nixpkgs continues to grow so the number of things not covered keeps growing smaller. But when you do encounter it, you can just create your own package and pull it into your flake.

AI makes this even easier, but you can usually find a similar package on nixpkgs and just modify it to suit the needs of that particular application.

I'll say this. Recently I reinstalled arch to see if I liked the freedom of it more. Within a week I reinstalled NixOS (which thanks to version control meant I was able to reinitialize it to be back in the exact state it was in beforehand).

Yeah I have no idea what I'm doing but I tell an agent to add such and such as a package in my flake.nix and it does it. I did this for getting the font I wanted in a LaTeX project even.