Control isn't binary. Facebook can exert much control over discourse while still being vulnerable to powerful actors.
The idea that I'm primarily disagreeing with is that Facebook, Twitter, et al. can be hegemonic in a user-populated space. I don't think they can. They can certainly exert large amounts of influence and constrain it, but it's not monolithic and they don't control it. Federation only makes that influence more invisible. It certainly doesn't remove it.
Just because not all problems can be solved with Mastodon, and the like, does not mean they are not worth pursuing.
Are humans in large numbers capable of interfacing with individual human beings without engaging in pernicious behavior? The answer, as anyone online in the last twenty-five years is a resounding no. Are humans in large numbers capable of behaving immaculately when it comes to preserving their own or their customer's privacy? Once again the answer, as anyone online in the last twenty-five years (and several decades longer if you include proto-business networks) is a resounding no. If you add progressively more humans to anything, does the output improve? If the metric is human satisfaction, the answer is no. If the metric is the rate of return in a Ponzi scheme, then yes, okay, you've got me there. The cause of almost all problems is solutions.
As far as social media goes, it's literally designed to use people to promulgate human-motivated pseudo-information for as long as humanly possible. It's not for "socializing" or "meeting people" in the same way that TV shows and movies aren't there for entertainment. It's to sell the viewer's attention to people that have anything but their interest in mind. Moving to federated enclaves is just further deregulating an already throughly pernicious industry.