For me, for gaming, the full-screen console-like experience is part of the appeal. SteamOS has full-screen Steam, but it doesn't boot into it. Plus, Gamescope has some nice performance measuring/management tricks that regular Steam doesn't provide.

If you just want Steam on an OS then installing Steam will do fine, but it's no "real" SteamOS experience.

Another part of the appeal is how stable the updates are thanks to update mechanism (and locking users out of the system config by default so they can't break their Linux installs with outdated scripts from askubuntu.com).

I run a similar setup for steam on linux. Overall I'm very happy with it in that it plays some old games I like to play from time to time (dota2, portal2, oxygen not included). Some games are still windows/macos only unfortunately, afaiu it's up to the game owners which platforms they serve. Shout out to the wine and lutris projects which both help make gaming on linux better since a loong time.

> Just install Steam on any distribution (I use Fedora) and it all just works like SteamOS - Proton use is transparent.

Absolutely! And if you really feel you need a truly SteamOS-like experience, there's entire distros (like Bazzite for example) devoted to replicating that as closely as possible for desktop PC users.