I think the major change was Steam and the Steam runtime rather than Proton, which solved the library fragmentation problem. Since then we have seen a considerable amount of same-day releases and native ports on Linux.

It didn't solve library fragmentation as much as it showed the solution that was always available and already used by most ports before the Steam runtime existed: to bundle all the libraries you need besides system interface like libc, libGL, etc. This is really no different on Windows.

> Practically, no one did this before Wine/Proton.

Oh come on, that's a huge exaggeration. There are thousands of native games available for Linux and Wine/Proton had nothing to do with that. Finding something to play hasn't been a problem for a long time if you are interested in a wide enough range of games.

Steam did make a big contribution to that but that was before Proton - if anything, Proton might have slowed down the number of new native releases. What Proton solves for people is being able to play specific games they want to play, like for example the latest popular AAA game that everyone is talking about - for that it's not enough if there are x% of games available no matter how big x is.