It's a host DRM, and many games also integrate with steamworks, making it an embedded DRM that can prevent your games from launching without a connection even if they otherwise wouldn't need one. As others have said, this is inferior to both GOG, and physical media, except a large percentage of physical media now also does not function without the aid of online DRM.
The DRM built into steam is pretty purposely nerfed. Supposedly it is trivial to bypass, which is why many game companies put 3rd party DRM in as well. If valve dies tomorrow, it will be way easier to revive most of my steam library than anything on origin or EA whatever-its-called-this-week.
They also just have like 20 years of clear results, consumer non-hostility, and goodwill
I'd say the cd key and cd check of physical media is more anti-consumer than Steam. Of course there were third party patches to remove the cd check, but that's no different than making a way around steam drm.
