But most people use Steam anyway, I hear you say. That's true, but you can still own your games on Steam. Very easily, in fact! Steam doesn't apply a hard DRM for games on their platform, you can bypass it and play your games offline without the launcher if you know what you're doing.
Because PC is an open platform, people have figured this out and will continue to figure out bypasses in case things go south (which they haven't so far, thankfully). All you need is to get something called the Goldberg Emulator, replace the SteamAPI file, then add an app_id.txt file. Done. You can play any Steam game offline (assuming the publisher didn't put their own DRM like Denuvo). I've done this a lot, and it is legal as long as you don't share your game to other people.
This part bears repeating anytime someone says "Valve killed ownership". They can break the trust that is formed with their customers at any time, but so far they have not.