So you have particularly skewed perspective; you should try a bit of operations, or at least devops, to normalize it.
> Arch perfectly suits my needs
Good for you. You just need to realize that you are minority. Do you notice that Arch is not the dominant distro? There's a reason for that.
> where as Flatpak/Snap... cause excruciating pain every time I'm forced to interact with them
You are holding it wrong ;)
> but Nix
Nix is not exactly a typical immutable system; it has strong opinions about many things, that other systems don't. You can't evaluate other systems through assuming they are like nix.
Nowadays, even MacOS is immutable and people live with it just fine.