And Proton's not the end-game: it's a solution to the chicken-and-egg problem. Most people (like yourself) don't see Linux as a viable gaming platform largely because of the lack of games available, and therefore developers don't invest in Linux support, and thus there continue to be few games available for the platform. The promise of Proton is to make Linux good-enough for some gamers, thus increasing the Linux player-base, making Linux a viable target for 1st party titles.
> It's never going to get to an equivalent level, because Windows' gaming technology keeps moving forward.
That's not really accurate, and hasn't been for some time. For years OpenGL has been on-par with DX in terms of what it can do for some time and the story has only gotten better with Vulkan. Just look at Doom 2016: it was a high-profile AAA game built entirely on an open-source graphics stack (OpenGL and Vulkan) and it was one of the best-looking, best-optimized titles of the year. The main "edge" Microsoft has in terms of being able to bring the best games to its platform has nothing to do with a technical advantage: it has everything to do with industry momentum and incentivizing studios and industry professionals to use their proprietary technologies.