> I've found the Nix ecosystem to be lacking, missing packages, wrongly built packages
This is an interesting problem you've faced, their marketing claim is that they have the most comprehensive catalog of packages (and I'm inclined to believe it). I very rarely run into broken packages, and that's usually resolved by using a stable release for that specific package - and it's not like my usage of packages is lightweight (7292 lines of nix config). That's on NixOS (and Silverblue, and Ubuntu) at least.
That's on NixOS, but on other distros there are issues. When I tried nix last year, installing alacritty, for example, required an opengl wrapper. Neovim couldn't compile plugins without environment hackery.
Things just work with pacman or dnf.