I have personal experience with that problem. Recently I had to install a secondary windows boot just to play W40K Battlefleet Gothic Armada in drm-protected COOP!

But DRM is a problem in and of itself. Something which linux gamers can't even change by refraining from buying, with their mighty ~1% market share.

Also, the companies who rely that heavily on drm are not really in the business of providing native linux clients either. So proton can hardly be a hindrance for adoption here...