I just wish they had to toggle to use proton by default for all games, regardless of if a Linux version exists. There have been several games where I ended up with the buggy abandoned Linux version (Rocket League is a particularly egregious example of this) instead of the much better supported Windows + Proton version.

An interesting example was Borderlands 2. The game originally had a native port by Aspyr, which worked quite well. 5 years pass and they release a new update and DLC - but they neglected to update the ports. 5 more years pass, then at some point in the past year or two they just plain removed the native Linux packages. They didn't announce it or anything so not 100% sure when. So these days when you install it you always get the (updated) Windows build under proton.

I'm a little sad we lost the native version, but on the other hand running it under proton just works, as I'd been doing for years, and the game would never have been updated otherwise.

Another example of this is Left 4 Dead 2, ironically made by Valve. The Windows client is far better, but unfortunately Valve hasn't fixed a bug that prevents joining VAC-secure servers when playing on Proton. This means you need to find an "insecure" server or host your own game.