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
This is changing. Valve is actively working with hardware manufacturers to get SteamOS on a number of systems other than the Steam Deck. You can buy a Lenovo Legion Go S with SteamOS today[1], and Valve will be supporting SteamOS on the Asus ROG Ally in the future[2], whether Asus partners with them or not.
because official SteamOS doesn't support the Xbox Ally X yet. It's safe to assume that official SteamOS will eventually support the Xbox Ally X, but it's not there yet.
Valve moves slowly to add support for more devices, etc, whereas the Bazzite devs can move faster.
e.g.
Bazzite does a weekly release of a stable OS candidate, whereas Valve often takes months, if not up to a year, for to release a stable-channel OS update.
Edit:
Also, Valve tends to wait for proper kernel interfaces for functionality like controlling TDP, RGB, fans, etc. Whereas Bazzite devs are fine with using tools in userspace to directly talk to hardware, etc.
While I do think Valve's approach is better for long-term maintainability, Bazzite will always have the speed advantage because it can hack together a solution via userspace applications.
Not sure what the specific benefits of SteamOS are. It’s forked from Arch, I don’t know what Valve changes. Maybe slightly better hardware support for Steam Deck? I run Steam on Fedora on my desktop and have no issues.
I don't run SteamOS but I run Bazzite on my desktop, the main advantage of running these immutable gaming distros is to have a fuss-free gaming experience - my PC boots straight to Steam, and I never ever have to worry about OS updates or other maintenance tasks. Basically I get to enjoy a console-like gaming experience.
I work as a sysadmin during the day, fixing PCs and stuff, and I really don't want to continue doing that after I get home - I just want to pick up my controller, put my feet up and get straight to gaming without having to worry about updates and other PC annoyances.
The best part is, if on the rate ocassion an update breaks something,I can easily boot straight to the previous image from the boot menu, without needing to run any commands or do anything special post-boot. And with Bazzite (and other uBlue distros), I can go back upto 90 days worth of images (3 previous local images + older images pulled from the cloud). I can also pin a known "good" image so it'll always be available in the boot menu. Essentially I get a rock solid unbreakable system, which is great because after a hard day's work, I really don't have the patience to deal with any PC issues at home.
SteamOS is very different from Arch. There’s almost too much to list here. But it uses an image based read only OS, a fully custom wayland desktop environment/compositor, does not have pakman, software is distributed either through steam or flatpak, OS image updates have their own mechanism. And a whole lot of preinstalled drivers and software for things like controller support which typically don’t come out of the box on Linux distros.
The whole OS is made for controllers, no need for a mouse/kb for anything.
Also, why didn't they install SteamOS directly? https://help.steampowered.com/en/faqs/view/65B4-2AA3-5F37-42...