@j I don't know where the idea of "masto is an alternative for twitter" came from. I think the line is deceptive, but it has been repeated over and over again everywhere. As you said the websites and apps look similar, but that's it.
The combination of people leaving twitter, because it got worse and mastodon (not the other fedi services) intensely promoting itself as an alternative to twitter was a bad move for the fedi. I am happy about many new people here, I'm not happy about the deception.
I'm also not happy about the dominance of mastodon in general and mastodon.social in particular. I think diversity and decentralization should remain main principles of the fedi. Communities of various sizes that can interact with each other without one dominating place. mastodon social and its team is accumulating enough power to break the fedi.