I do not think it is a very good analogy. I do not see how this would turn into a broadcast medium. Though I do agree it can feel less accessible and there is a risk of building echo chambers.
Not so concerned on that–people being able to establish their tolerances for whom they want to talk to is fine with me. But if the system goes towards allowlists, it becomes more cliquish and finding a way in is more difficult. It would tend towards centralisation just because of the popularity of certain posters/instances and how scale-free networks behave when they’re not handled another way.
It’s most likely a death sentence for one-persone instances. Which is not ideal. On the other hand, I’ve seen people managing their own instance give up on the idea when they realized how little control they have over what gets replicated on their instance and how much work is required to moderate replies and such. In short, the tooling is not quite there.
I run my instance and that’s definitely not my experience. Which is of course not to say it can’t be someone else’s. But something, in my opinion not unimportant, is lost when it becomes harder to find a way in.