A few last thoughts about Facebook and Threads.
Their claimed user numbers are obviously bullshit. Even taken at face value, millions of people clicking a new button is not millions of people using a new service.
Second, their business is serving ads only. They have as an organization proven, repeatedly, that they will accept any adverse human impact up to and including genocide as long as their graphs go up. Their stated intentions are irrelevant and believing otherwise makes you a mark.
Finally, there's not a lot of evidence that people will switch services en masse for any reason other than a tectonic failure of their current service. Microsoft spent billions on Mixer, it was one click away from Twitch and it didn't matter. Nobody is moving off Threads to the Fedi, but interesting posts from the Fedi will keep people clicking around in Threads.
The utility of the Fedi to Facebook is shelter from regulatory scrutiny with a side helping of content farming. That's it.