What you describe is, of course, possible. You can create a personal fidonet/usenet-like echo conference with nothing more than a bunch of e-mail redirection rules. But people don't want that. I checked.

There is no such thing as an "intellectual need". All the needs are fundamentally emotional. Mastodon addresses the identity need, it creates the sense of a community, and, as all the social media, it grants both cheap entertainment and immediate gratitude for conformity. It is a good "social network", it's just what we call a phenomena of "social network" is essentially shit.