I’m not sure I agree with the article. Arch is especially nice because it has best in class documentation and vanilla packages. The installation is a bog standard chroot and use package manager like Gentoo had for ages or an old school Debian. Arch is nice because it’s as vanilla as a Linux distribution can be. NixOS is the polar opposite of that: basically no documentation, weird behaviours everywhere, custom config…
Right, plus arch is rolling release which lends itself to never reinstalling the OS. The installation on my laptop is on its 4th hardware refresh. Rsync or brtfs send to a new box, modify the partition UUIDs, rebuild the initial ram disk, and you're on you're merry way.
But after about 5 years I would start having problems on my Arch installs and realize that some config I edited years ago is now causing a problem. I have to see if I should revert to the default config or merge in changes and if I need a new workaround. Overall the system was just accumulating cruft that ended up biting me. I never knew what configs I had edited and what the default was, experimenting was annoying forms of backing up the config, making changes and then figuring out what I actually changed.
NixOS is completely different because all of my "customizations" live in a Git repo. I have change history and it is trivial to remove things that aren't needed anymore and know I did a clean job. The concept of a re-install even doesn't even make sense. Every config change or update is just as clean as a re-install would be other than "state" like a database or my documents.
There are definitely a lot of differences between NixOS and arch such as many packages requiring patches to function at all or as expected. But "never reinstall" was a significant part of my ramp from Arch to NixOS.