There's still a difference — GOG provides you with downloadable installers you can archive, Steam doesn't.
I am a heavy pirate and I my favorite games come as raw files torrents with the crack pre-applied. Games these days (with DRM removed) simply execute no matter where you copy and move them they just work. The cracks themselves do not modify any registry entries or make the game write them new or differently because they simply do not use the registry. Games write their savegames in AppData or Documents and THAT IS IT. Installers are glorified copy machines with ads on them (GOG) for example. They copy files and put a shortcut in your start menu and desktop and THAT IS IT, they do not write special registry entries for a game to work. Again this has not been a thing for like 25 years. I think it was when SecureROM was a thing.
So yes some steam games actually come DRM free, and you do not even have to move them out of the original steam install folder you just need to execute the EXE without steam running and they work. So indeed it is in fact achieving if you simply keep the files somewhere. For game with basic steam DRM you can use a crack or use steamless that basically removes the steam DRM that is very basic from the exe and use Goldberg Steam Emu to emulate steam. You do all this after the fact so you CAN for all the game that to not have some advanced DRM like Denovo just achieve the games files and make them work later on without Steam.
I love steam but even if it can barely be called a DRM, it still is. People not into computer science will have no clue how to do it, and that's what matters when talking about owning your own games, you should not require knowledge to keep something you paid for
What other choice do you have if the game is only available on Steam?
Of course in an ideal world it would be available in a true DRM-free installer but in the real world you'll always need to reach for messy workarounds that just work. This is one of them and most people probably don't know that it exists.
Also that's the point. You purchased something you should not have to crack it to keep it.
Or are you misunderstanding the fact that you can just copy/back up the Steam game and play it anywhere. That's why I say many people have that misconception about Steam games
GOG on the other hand takes an active stance on promoting and supporting DRM-free games. Once storefronts like GOG disappear I don't think Steam will pick up the torch and fight the DRM-free fight. Once Gabe is no longer in charge it might just get overall worse for everyone, although fingers crossed Steam can at least continue as it is.
Is it? Is there even a list of them? I know some are, some aren’t. Sometimes it’s even mixed (e.g. Pathfinder Kingmaker is DRM free, the DLCs use Steamworks DRM). As you say, they aren’t promoting it, but I’m not sure they expose that information at all.