With all due respect to Nix/Guix, to me they swim uphill against the current of "worse is better" than UNIX is built upon. They are trying to tame the complexity of the world by making it declarative. A lofty, and a little too idealistic goal.
I much prefer the immutable approach (rpm-ostree) or even an unsophisticated approach like a Dockerfile, which is worse but much closer to the status quo, than to create a perfect world from scratch and hope that everybody follows the Light. Software is too large, complex, hacky, buggy and nuanced to expect it to fit into neat preordained categories. Because unless you do very simple things, you'll soon find yourself out of the happy path and have to resort to doing the hacky way anyway.
This is what some believe killed Lisp machines vs UNIX. I guess, like Lisp, in decades there will a vocal contingent of people lamenting the fact that we all run immutable Microsoft Kubernetes Ubuntu (MSKU) instead of using the more refined NixOS approach.