So I'm here. But even though my friends are awesome, I don't have any new ones I've made on Mastodon (unlike Twitter), and it is overall pretty boring and unlike Twitter it makes building a network feel like work. At the same time, it is of much less use for work. I have almost no Africa network, I have little interaction with journalists, and because the network is more closed, I learn less.
Whatever. It's fine but it's not a substitute for Twitter at all.
What it lacks is the ability to Quote Tweet, that is to add your own comments to what somebody may have said, which is often used in social mobilizing. It also doesn't have full text search. This was all done intentionally. But as a result, it's much harder to reach out of your networks to other people. I used Twitter to follow multiple social movements, as well as to learn about people in other countries. Mastodon isn't useful for any of that. And it doesn't want to be.
Mastodon does have a history of being Queer friendly (one app even asked me if I wanted to join an instance which was for Furries) but that gets used as a shield when people point out how unfriendly these spaces are to lots of other people. Heck, I saw parts of Black Twitter return to Twitter and say they would rather deal with the Nazis where they had community than stick around on Mastodon. It also does have decentralized moderation which makes it easier to ban Nazis.
Basically he was smug and entirely uninterested in the use of social media for social change, and was happy to jetison it all. He compared Mastodon to his private BB with guitar nerds where anything you wrote was read by 100 people and that was fine.
In this episode of #OnTheMedia where a senior Mastodon community member says basically that they limited things that caused virality because they thought that was one of the worst things about Twitter, and then kinda shrugs when he says something like "Of course, that means that Mastodon couldn't have supported social movements like #MeToo or #BlackLivesMatter." He also concedes that Black Twitter folk have been made to feel unwelcome, but ... eh.
TLDR: Mastodon is very white, male, status quo, global north, and designed in a way to limit its potential for use in social movements.
Mastodon feels very different from Twitter, deliberately. It is truly like Live Journal. It is about people who are happy with their social circle and who think of virality and discoverability as a problem. They just want to communicate with the people they know, and limit other things. Ironically, it is more like a private gathering than a public space.