Though, using asdf from Nix/Guix sounds a bit like trying to use a scythe while riding on a lawn mower.

I don't disagree - I turned back to asdf (which I use on most cases) after fumbling too much with defining Guix packages, under the thought of "what a pain in the ass, I'll try what I usually use"

I do think I'll take another crack at Guix at some point, but with more realistic expectations of not being able to know everything about it in a weekend :)