The point is that from a UX perspective, people want to be able to specify loose dependencies, and then for a constraint solver to then provide an overall set of dependencies where all of these holds.
You're saying "just use nix". Nix does not provide this. This is a fundamental feature of programming language package managers. I would love for Nix to have an interesting answer to this problem, but I think that if nixpkgs continues to exist in its current form (following more of an apt model), it will be hard for the Nix community to come up with an answer that fits well. Nixpkgs is mostly about distributing compiled assets, while programming language package managers are mostly about distributing source code. The important parts are different!
