Coping files to /etc doesn't require Guix. Installing applications and copying their respective config files doesn't require Guix. Guix seems worse for this than a repo of config files and a shell script or makefile, because of the required extra complexity

It's possible to have a full system setup with shell scripts. The only things I'm aware of people doing are copy-pasting the "install these packages" when setting up a system.

When it comes to reliably getting a system to an expected state, shell scripts aren't a popular solution.

Nix and Guix are more complex than not using them. I'd compare that to Vim/Emacs being more complex than Notepad.

My script installs configuration as well as packages. Guix is way more complex than my script, not only in part because I would need package a non zero amount of things to have it be feature complete with my shell script, and unlike your notepad vs emacs example, people don't seem to point to anything that Guix can do that my system can't, or the things they identify I do so rarely that it would be more efficient to do them manually instead of porting my system to Guix, like making containers.

Also not a popular way to configure a system? They are THE default way, that is being tried to displaced by various configuration management tooling and Guix, no?

If I wanted to sells emacs to someone on notepad I wouldn't have to resort to things as vague and hand wavy and dubious in value as reproducible'). I'd be listing features they lack. The Guix features I want I have, which is simple install of my applications and configs

You don't need Guix to copy files to /etc, you don't need it to install your applications and you can get a pretty reasonably easy custom install with a repo of config files and a script to clone and copy.