Most discs still contain the full game, most physical releases contain discs of the full game

Some physical releases are just an empty case with a code. Some Nintendo Switch cartridges are just license dongles for the game download.

You’ve never owned a game. You’ve only ever licensed a game. This is true for all software. Removing the physical medium of distribution just allows the copyright cartel the control it has always wanted over something you paid for. But they have been hoodwinking consumers over what “purchase” and “buy” and “own” mean. Technically speaking, any game company could send you a C&D and tell you to stop playing their game forever, your license is revoked, and if you ever played it again they could sue for damages. Doubtful they would, as I doubt it would be worth their time; but this does mean they have the right to just decide their work is no longer available and vanish all digital copies; and they could also make all physical discs stop working through system software updates.

Sorry to kind of ignore your question, but I think it misses the point.

Even with only the partial game data on the disc, the disc still held the rights to the game. Therefore, the rights were transferrable. That is to say, you could still sell your disc and it would have value to the next owner.

When you are forced to buy the game directly from the PlayStation store, your game license is no longer transferable. You can't sell your old games, and you can't buy used games from someone else.

All of them contain the entire game. The only functional difference over the early days is that the game data isn’t read from disc while you play.

Not true for the majority of games, however there have been a few that have done this or something like this.

Been seeing this sentiment a lot in the wake of the news and want to stress, most games still come on disc these days. FF7 Rebirth, for example, is so big it comes on two.