> I just want to list what I want and let the tooling make it happen.

That's just what Nix does?

It's very much more declarative than any system I've seen. Yes, k8s turns your declarative manifest into running processes, but how was the image built? There's a huge gap there: you refer to container images by name, not by a description of the software you want them to contain, and then hope that some other process has built the image correctly. Nix can close that gap and take declarative all the way from the service manifest down to the git commit of the compiler used to build your binary.