Is anything around forever? What kind of argument is this?
Proton works by wrapping Windows calls to Linux equivalents, which have been improving and becoming more robust as a result of this work. If the Windows game ecosystem collapses (How? When? It's literally never been more popular) then those equivalent APIs can be targeted instead. Meanwhile, the absolutely massive PC back catalogue, the platform's greatest strength, remains playable.
Proton works by wrapping Windows calls to Linux equivalents, which have been improving and becoming more robust as a result of this work. If the Windows game ecosystem collapses (How? When? It's literally never been more popular) then those equivalent APIs can be targeted instead. Meanwhile, the absolutely massive PC back catalogue, the platform's greatest strength, remains playable.
Where's the downside?