You might not have know, but Steam game can be without DRM, meaning there’s no need for the client to be running for it to be able to run. I’m not sure how up to date this is, but here’s a list for some of the game. The client are required only when the dev use the overlay or any steam function. You can even find a list of patchable game to make it drm free.

Nope, DRM is optional. You can install some games (Rayman Origins, for instance), copy the directory to a new computer with no Steam and run the exe. Steam also has Steam Input, but no one says it’s just a gamepad driver.

It’s only a little bit more DRM than GOG. It doesn’t automatically adds a DRM layer to all games. There are tons of games that you can backup by simply copying their folders. Even if the DRM layer is added, it’s very light, can be cracked easily and does not add any measurable overhead.

Steamworks is probably a major thing that makes the games rely on Steam client (and it’s not technically a DRM). But that’s up to developers to make the game work without client if they want, and the functionality often adds a lot of value. This makes the client a part of the product you get, and its value will degrade if you break the client. Some examples of such valuable functionality are overlay and steam input.

Its not that steam is good, its just that everyone else so extremly dumb and incompetent. And GOG only has a very limited catalogue