I think what many folks really want from "federation" is a situation where no one party has more than 40% (or 10%, or whatever) of the network.
That is a powerful and special property! Fediverse has it today, and most networks don't.
It is different from adversarial interop though. There are open systems, like email (gmail) and git (github) which have sort of lost this. I still think the interop in those systems is valuable.
