You can not-quite-trivially download all versions of a game that have been uploaded to steam, as long as you own the game. And that's a download like as an installers you can run, not just overwriting your current active steam install.

I actually rely on this quite a lot, indirectly. Beat Saber is a fun game, but it doesn't support a lot of fun features, like walls with boundaries that aren't aligned to the coordinate system. There are mods to add those features, but they haven't all been ported over to the new line of the game since it upgraded the version of unity it's using. So I use one of the mod managers that supports, among other things, maintaining multiple versions of the game in parallel so you can choose what you want to do when you start a game. This feature very explicitly relies on downloading older versions from Steam. Because that's a thing you can do with Steam.

In the same week that Sony announced they'd be ending production of optical media, they also removed hundreds of movies from user libraries that they'd lost the right to sell. I don't really care if they have yet to do the same with games - they've demonstrated they're willing to remove access from paying customers for their own reasons. And there's nothing the owner of a locked-down console can do about it.

Steam exists in a different universe than digital-only games from PSN. Conflating the two because they use the same method of delivery is ridiculous.