none of the major providers will deliver your email without your mail server having first built a reputation

There are definitely major, and easily-abusable "features" being implemented by the major email providers, but I don't think your statement is correct. I have a Hetzner server, and I can receive email from it (to Gmail) just fine, as long as I have SPF, DMARC, and DKIM set up. I can also create a new server with a new IP and not have any issues. The issues may arise with shared IPs/ranges that are also being used by spammers. Otherwise, if you're planning to send bulk email you just need to warm up the IP.

i think you may be mixing federated and small-web feel there. there exists the ability for individuals to have functioning email servers although it is difficult but fair considering how much of the world is reliant upon it and opposing it with various kinds of attacks. i dont thimk it requires many individuals to have their own servers for it to be considered federated, the fact that we have dozens of relatively big email providers to choose from who prioritize various different things is enough to cover the majority of peoples needs and i think that is the threshold requirement for a sufficient self sustaining federated network. regardless of that, if you compare this outcome of email as of present to lets just say a platform like discord whose goal is to facilitate messaging between people, you can evidently say thst emails outcome is better than the proprietary service that discord is locking people into and not making alternatives ways of accessing the service a simpler process.