That's true on paper, but is glossing over a huge issue: the Fediverse is strongly politicized. Mastodon instances are under pressure to not federate with undesirables, under threat of being defederated by others. As a result, you have one "primary" network of instances whose admins and members either subscribe to specific kind of political extremism, or are at least willing to acquiesce to it for the sake of the users to have anyone to talk to, and a forest of small clusters. The "primary" network and secondary clusters don't talk to each other, and associating yourself with the latter is a quick way to be booted off the former.

Technically, this is federation working as intended, but it's not as diverse and inclusive as it advertises - on the contrary, it's more like a HOA that has a right to ban condo owners from talking to each other.

It's a nice place to be when you're not into politicking, but then so is Twitter, so it's not that big of a win. A more compelling argument for Mastodon is that it's community-funded, so it's not out to sell your eyeballs.