Mastodon is absolutely thriving. I get you want to be a contrarian but the fediverse is loaded with people who left X and never went back.

I know a considerable number of people who abandoned Twitter for either Mastodon or Bluesky and haven't gone back. It probably depends on what circles you run in. There are some people I know who keep Twitter accounts because it's used for professional networking, for example, but they're in specific fields.