Yes the maximally centralized form of a protocol like email is the one we have now where a few large actors can collude to cut you off from large swaths of the network.
However, that’s different than a singular actor, but more importantly, nothing is stopping a counterforce from coming in and correcting that regime. It’s possible we may see email revert to a less centralized form over time as various people choose to prioritize working that problem (and can make headway, because of how email works.)
The point is email as a protocol is extremely open, but email as a network is quite centralized. There aren’t any great options here because buildings a system is easy but interfacing it with the real world and all it’s laws and bad actors is hard.
What people forget is interfacing with systems designed to operate in the real world is at best an abstraction over this difficulty and eventually it gets exposed for the mess it actually is.
