Arch isn't unstable. Users mess it up by installing a bunch of random crap from the AUR or fiddling with system files.
SteamOS addresses this by making the root level filesystem immutable and guiding the user to install containerized (flatpak) apps.
Like many GUIs it makes it so you don't have to remember and type a bunch of commands to carry out basic tasks. I especially find it convenient for checking logs. But no unique functionality compared to CLI. So it's a matter of preference.