I know indie web camp has a thing against hosting services and probably the small web people would also say blogspot and wordpress and wix are too corpo.
So imho drawing the distinction at not requiring payment/login works as an open web definition. And if self-hosting is a requirement for some people, there are other terms to use.
Youtube, Substack, Medium and the like are open-ish. They're far more of a heavyweight platform than a web host or publishing tool. They could become walled with the flip of a switch. And they can be ad-walled which is testing the limits of openness.
