Is it? On GOG you can download games without installing their proprietary client (there is also a libre alternative called Heroic Games Launcher, but that's made by the community). Itch has a libre client and it's also optional. Both those platforms don't put DRM in games, unlike Steam.
Steam has forced updates. This means that game developers can push an update that for example deletes content from your game and as far as I know, you can't really refuse it.
On a page of every game that is sold on Steam, you will see text that says "Buy". But I'm pretty sure their ToS says that you are only renting games from them. So they are misleading their users.