SteamOS runs its own infrastructure and is more than a static set of scripts and dotfiles on top of an existing distro.
Steamos is a mirrored snapshot of arch (like omarchy) + bash and python scripts (like omarchy) + their own shell (steam running on top of gamescope for steamos and a custom quickshell based one running on top of hyprland for omarchy) + modified upstream kernel (both steamos and omarchy)