I'd say way more than that are DRM-free. Of course most of AAA releases do have.
Steam installers are just text files, so those can be manually applied too (and if steam went down, I'm sure someone would make solution for that).
Please go test the games in your library and then come back to me. I actually check this on pretty much every game I own via Steam. Even indie titles--heck, even titles that are available DRM Free on stores such as GOG--won't start up on a computer without Steam installed.
At this point in time, I'd say its more likely that MS kill W32 compatibility in favour of UWA - nuking your entire catalogue without a fuck given what kind of drm it may or may not have once had - than Steam go down and nobody provides a working backup to handle that.
If that happens, I will set up an offline Virtual Machine running legacy Windows, and will continue to play all of my DRM-Free games that way. It won't be able to connect it to the internet for the same reason you can't connect unpatched Windows XP to the internet today, but my DRM Free titles will still work.
Honestly I wish Steam had a box in the features section for "DRM Free" so that developers could actually advertise the fact their game on Steam can be run without Steam. Lots of smaller scale developers don't bother crippling their game in any way and it is kind of annoying they can't promote it as a feature.
Most of Valve's own games include Steam DRM--try launching Portal 2 without Steam installed. I don't think Valve particularly
wants to encourage DRM Free titles. They want everyone to have to keep Steam on their computers.
And y'know what? That's generally okay by me. Sure, I try to avoid buying games on Steam whenever possible, but on the whole Valve's actions are at least honest and up front.
Gog Galaxy is so unobtrusive, I don't care.
It's just a game client, OP. Not really a big deal.
Okay, let's step back for a second and review the past couple of years:
Some Users: We don't like Steam. We want to play our games without any clients. How can we do that?
GOG: Come over to our store! We have no DRM and no clients, so you'll like us more!
Users: Yay, thanks GOG!
GOG: Hey, we've just released a client, because a lot of people actually like them. But don't worry, it will always be optional!
Users: Huh, okay, sounds cool as long as we never have to use it.
GOG: Hey, we're now going to bundle our client with most of our games, but don't worry, we'll warn you first by whispering so softly that most of our customers won't be able to hear. Oh, and you can still get the old type of installer, you just have to jump through a bunch of hoops every time you download a game.
Users: This sucks.
Other Users: But GOG's client is great, why wouldn't you want it?
GOG Galaxy could be the most refined piece of software in history, and I
still wouldn't want to use it.The entire reason I come to GOG is because I didn't want to use a client. So why the heck is GOG pushing a client on me?
The fact that GOG is still better than Steam in this respect is neither relevant nor up for debate.
GOG needs to step back and reconsider what differentiates them from Steam. It certainly isn't their library, which is surprisingly good but still crap compared to what's available on Steam. DRM Free is wonderful, but that means different things to different people. To me, most of the appeal of DRM Free games is the ability to easily install that game, by itself, onto any computer without any extraneous BS.