Disc is a manifestation of right. Without this they will screw people without them even noticing

Discs do matter in one way. I don't think I have ever seen a digital "purchase" of any significance which I could resell or gift at a later time. Some "in game" things are resellable, but only within the game's ecosystem. All digital games, music, movies, ebooks, audio books, etc are not (AFAIK).

So if I get tired of my DVD movie collection, I could sell it or give it to my kids. If I ever decide I'm too old for the retro game cartridges I have, they could go to future grandkids. But my GOG games or Bandcamp music is stuck with me forever (legally speaking). Nobody would know if I "gave" them to my kids, but there certainly is no way to resell them.

Now this is still a rights issue, but physical media makes this easy (outside of keys/DRM as you point out) You always have the right to hand on a physical object.

It's a proof of purchase that can be transferred without approval by (or knowledge of) the original seller. There is literally no equivalent possible with digital sales, unless you accept flawless, pervasive DRM everywhere.

It doesn't have to be a disc. It almost certainly does need to be physical.

Discs matter because centralized digital distribution is what is eroding your rights. The medium's the message.

It's the malleability and ephemerality of digital content that has enabled not just restricting people's rights, but destroying the authenticity of media by arbitrarily replacing its content. The reason Amazon could delete 1984 from your Kindle, is its digital nature. Nobody, except you, can delete a book from your shelf or change its content.

Legal rights don't matter if the other party is ever liquidated, or otherwise unable to meet their obligations.