They're completely fungible, and the "damage" to the manufacturer, even a potentially contrived "piracy is theft" argument doesn't hold up. You already bought the game, the developer got paid as much as they would have if the service stayed up. Just because the service provider shuts down doesn't change those facts.
That's like saying that if you're watching a blu ray rip of your own purchased disc, it isn't the same product you bought. Technically correct, but it's completely legal to rip your own discs(at least in the EU, can't comment on other countries).
My issue with "just download a crack" is that I have to spend time hunting down the crack, and I can't be sure the crack won't include malware, or won't introduce bugs which only appear later in the game. The last of these has happened to me on multiple occasions. A cracked game is no longer the product I bought.
By contrast, when I buy a game on GOG, I get a product that is DRM Free and will work forever—and because it's the product I actually purchased, I receive some minimal level of assurance from the retailer.
I would feel somewhat differently if there was a single "universal" crack that worked on all Steam games, or even which worked on 95% of Steam games and failed in a predictable way on the remaining 5%. This is the case for iTunes TV Shows, and so I have no problem paying for those, because I can run them through some software and I know the DRM will get stripped correctly every time with no quality loss. I'm not aware of any such software for Steam games.
You are correct of course. My point is that if Steam would disappear, a technological solution would appear to play your games. Just like even once every single PS1 on the planet turns into dust, we can still play PS1 games by other means. With stadia, this will never happen because you can't get a copy of a Stadia game I'm the first place.
I just question how much that matters in practice. In both cases, you can theoretically replace the game you bought with a pirated copy.
All PS1 games have been archived, yes, because the method of ripping a PS1 game is consistent across every title, and the total number of games released was relatively small. That's not the case with PC games today, and I think it's virtually inevitable that a lot of indie games released exclusively on Steam will eventually be lost to time. As will many of the indie games released without DRM on itch.io—but at least any game you downloaded from itch.io will be playable forever.
You can argue cloud gaming is even worse. Maybe so, but at least it provides a lot of extra utility, since you can play on low-end devices. Steam provides automatic updates, that's kind of nice I guess, but not in the same class as running Assassin's Creed on your phone†. (Even then, I personally wouldn't pay full price for a game I can only run on someone else's servers, but I understand why someone else might.)
I don't like Steam.
† In theory. I've always found cloud gaming has too much latency for me. But in theory, if it worked perfectly—which perhaps it never will—the promise is nuts.
You seem to be saying (and be certain of) that in the EU, were Steam to be discontinued, it'd be completely legal for you to download a crack to bypass the DRM for the game you were previously licensed to play through Valve's platform. Is this established as a matter of law? Could you share any links on the topic?
If it wouldn't be legal, then downloading the crack to the game you paid to play through Steam but can't anymore would presumably be just as illegal as pirating the whole game to begin with. Did you really purchase the game or just an indefinite (but not necessarily eternal) license to play it?