"please tell me why I still should support DRM-free if it still is up to the publisher what I can keep and what not?"
I don't want to be 'that guy' who says "yes, but..."
, but the truth is DRM-Free gives you the opportunity
to prevent publishers from altering / removing access from your content (by backing offline installers up). It's never given any buyer permanent control over the cloud server of the store they bought it from. This is true on Humble (who scrapped several DRM-Free direct downloads in favour of Steam keys), it's true on Steam & Epic (who have both added DRM to some initially released as DRM-Free games in a patch) and it's been true here on GOG even before Wolfenstein 3D. (Eg, GOG used to sell Operation Flashpoint Cold War Crisis GOTY (with 2x DLC's, Red Hammer & Resistance) then that got removed and replaced with ARMA Cold War Assault (only 1x DLC Resistance with the Red Hammer campaign completely stripped out and missing). This is why some of us 'kick up a fuss' over the "2nd class citizen" thing regardless of how it upsets some to 'keep hearing about it'. Achievements, cloud saves, Galaxy rollback, even Galaxy itself can disappear server-side *poof* just like that. Offline installers are the only thing here immune to unwanted alteration by GOG or the publisher that actually gives tangible meaning to "DRM-Free" or "game preservation" in the long-run.
I hope you do get it sorted though. Perhaps some hope comes in the fact GOG did actually go back and re-add some .exe's of DOS games they previously stripped out in the process of adding ScummVM, so maybe they'll reconsider here with W3D here if enough people kick up a fuss.