I just made the jump to Ubuntu. You don't need a Steam Deck or Steam OS. Steam works just as well on any Linux OS. Proton is the real star because it deals with the compatibility issues so well.
That is true. But without the Steam Deck, Proton support would also be lower. And that's the main reason why I hope that they continue their current path, because I also get a lot of enjoyment out of Proton on Ubuntu.
The genie is out of the bottle now. I love SteamOS with its ease of use and steaminput integration, but theres already a ton of open source projects building on what they started that would totally still be able to out perform microsoft even if valve stopped updating steamos today. But every indication seems to be that thats the opposite of their plan, as they're extending steamOS support to other handhelds and devices officially now.
I think Valve does a lot of work on Proton to make it work this good because of SteamOS. And that's the main reason I say this. Because a lot of Linux gaming is possible because of the work they put into it.