Earlier quoted context omitted.
Mastodon is essentially centralized — you just pick who you trust with full centralized authority before they have a change of heart, fail, begin rent collecting, whatever. Nobody seems to understand how difficult it is to make a system that can guarantee its neutrality within the protocol. (Sorry HN: it requires crypto.)
Then host your own instance. Your definition of "centralized" as "optionally requiring any trust at all" is pretty broad, and sweeps up even email.
The same is definitely true for email. There are many providers, so "centralized" is a bit of a loose label, but running your own email server comes with non-trivial pitfalls that keep most people away.