I think you use "federated with" in a different sense than most people do in these discussions.
A newly created Mastodon instance by default federates with everyone in that allows messages and following from and to every other instance.
But it's federated timeline has no posts from other instances, because that view only shows posts that the instance actually sees. It only shows what people on the same instance actually follow, because otherwise there is no reason for the posts to be sent to it.
That would explain a lot of things and also clears up a lot of things for me, too! Thank you. I guess a better phrase for what I'm trying to describe is a lack of discoverability, then.
A newly created Mastodon instance by default federates with everyone in that allows messages and following from and to every other instance.
But it's federated timeline has no posts from other instances, because that view only shows posts that the instance actually sees. It only shows what people on the same instance actually follow, because otherwise there is no reason for the posts to be sent to it.