AIUI (I don't have any of this hardware) SteamOS is really meant for the Steam Deck; while there's "basic support" for the ROG Ally, it's not their focus. Bazzite seems to be quite happy to support everything, and AIUI it's frighteningly close to SteamOS (the same customizations, etc.)
It's not "we have SteamOS at home" - it's more like RedHat vs CentOS
It's not "we have SteamOS at home" - it's more like RedHat vs CentOS