Yup I’ve spent a good while running Deck in desktop mode compared to my laptop running Manjaro, and so far the only thing I’ve noticed is that the Deck has that handy “add to steam” context menu item that automatically sets a 3rd party game to run in proton through steam.
And there’s an AUR package for that.

So unless there’s something more I’ve missed, Manjaro + that package gets you the entire desktop SteamOS experience on any device.