I think the opposite might end up being true. With a critical mass of users on Proton, developers end up being pressured to make sure their games work properly

I think the opposite might end up being true. With a critical mass of users on Proton, developers end up being pressured to make sure their games work properly in it. When a substantial number of their users have a problem running a new version of their game, even on an unsupported platform, they tend to do something about it. There have been a few instances of this happening already for some high profile games.