alt Hacker News> will end up being the only mainstream Linux desktop because of its corporate backing
Ubuntu, Fedora, SUSE, Pop!, Deepin (and the list goes on) all have corporate backing. Steam is a well-known consumer brand though, so that might make a difference.
I don't think the usual distros care about the desktop experience as holistically as a long-term consumer company that Valve is. Otherwise one would expect Linux distros would be much better than what they were even 10 years ago.