For a few years before I eventually got a Steam Deck, I played a lot of games that I bought outside of Steam, and over the past decade, the experience of doing this on Linux has massively improved. Plenty of their improvements get upstreamed to Wine, and there's nothing stopping you from obtain proton (or even one of the various unofficial tweaks of it) to run games that you don't buy through Steam to get the benefits that aren't upstreamed (or haven't been yet). The article itself mentions that they've implemented a driver for Mesa that has equal or better performance on ARM than the proprietary one from Qualcomm.

It's not clear to me what you're attempting to convey by saying the Steam Deck being the only product they have that supports the open source vision. The Steam Deck is the only new hardware product they've had since 2019, when they released their original first party VR headset that presumably is being replaced by the new one. Other than that, the only other hardware products they've ever worked on were earlier headsets made by other manufacturers or the previous iterations of the other two products announced alongside the new headset. From that standpoint, you could make a credible argument that the only product they even have right now that benefits from the open source work they've done in the past six years they did is the exact one you say supports this vision.