> unless you run nix-collect-garbage periodically
nix.gc.automatic = true;
nix.gc.options = "--delete-older-than 10d";
I've found this useful to eliminate the rebuild loop: https://kokada.dev/blog/quick-bits-realise-nix-symlinks/ It lets you make the config of the program you choose a regular mutable file instead of a symlink so you can quickly iterate and test changes.
> In contrast, Arch Linux simply downloads prebuilt binaries via pacman or an AUR helper
If a binary exists. A lot of AUR packages I used to rely on didn't have a binary package (or the binary package was out of date) and would have to build from source. On nixos my machines are set up to use distributed builds (https://wiki.nixos.org/wiki/Distributed_build). Packages that do need built from source get built on my server downstairs. The server also runs a reverse proxy cache so I only need to download packages once per version.
Distributed AUR builds are possible on arch, but they require a lot of setup and are still fragile like regular AUR builds, your only choice of dependencies are what's currently available in the repos.
> On my machine, regular maintenance updates without proper caching easily take 4–5+ hours
It sounds like the author may be running the unstable release channel and/or using some heavy unstable packages. Which might explain a lot of other problems the author is having too.
Back when I used arch, I found that as time went on, my system would sort of accumulate packages. I would install $package, then in the next version of $package a dependency would be added on $dep. When I updated, $dep would be installed, then eventually $package would drop the dependency on $dep, but $dep would remain installed. I would periodically have to run pacman -R $(pacman -Qtqd | tr '\n' ' ') to clear out packages that were no longer required.