Tim Berner’s Lee and the Solid project have a good answer to these issues I think. Everyone owns their posts and likes and comments and friends etc. Any new platform can spin up and instantly compete because they just have to make your data more useful to you. It’d be like you owning all your music online and Spotify is just an interface, if you don’t like it you can jump to Apple Music. Or make your own or download some random app off the web that does what you want. The reason a new social network can’t just compete with Facebook is because they have all the data, if the data could stay with us then new platforms offering news ways of interfacing would be popping up all over the place. https://solidproject.org/