I understand those concerns, but I’m not sure if this really improved the security of mastodon, an inherently very insecure software, and it definitely deprived us of a useful tool. Defederation works at stopping spam, but I don’t think it really helps much when it comes to preventing people from seeing things you post. It stops a single server, but bad actors can just migrate to a new one, or spin up a new hostname.
I’ve had this issue before. My limited understanding is that your home server fetches copies of communities somebody on your server is subbed to. But if you’re the first person, it can take it a few hours to federate (took mine a day.)