SteamOS is Arch-based. Arch as a distros is extremely bare-bones. The main difference between all base-distros is how they manage their packages.
Sub-distros may opt to change how the package manager works; Manjaro delays updates until everything has been verified to be working and not likely to break anything. Yet, it is still Arch based.
There’s nothing about a base-distro that makes it inherently unstable. Arch is extremely reliable, depending on what you need it for.