I think there's a reasonable argument that the most stable Linux gaming API surface is actually Proton.
None of this is really going to change until we end up with a situation like the EA/Apple Store conflict: a major player unable to sell a game on Windows for some reason.
That is like saying the most valuable gaming API is Dolphi, MAME, or LinUAE.
Also, it's something of a pragmatic choice -- Valve did put major effort into native Linux games around 2013, but the effort fell flat for a number of reasons.
Proton is them trying a different path towards severing or lessening the Windows dependence, in my opinion.