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.