Thanks, this is extremely thorough and easy to understand. Very well put. I can see how for anyone with sufficient distrust of Meta and its users, it makes sense to defederate anybody who might serve as a relay between them.
In the meantime, I hope kbin can catch up before Threads starts federating, so I can just interact with people from here. Currently, there's people who I can't see/can't see me from kbin, not due to defederation but simple bugs in kbin's current ActivityPub implementation. If/when mastodon.social gets defederated, there's people I won't have any mechanism to speak to without registering a third account somewhere in the fediverse.