To me this is a flaw of federation in general and I really think the solution should be to defederate yourselves from other instances until further notice, and only federate with trusted communities.
With how Lemmy (and the fediverse in general) is currently set up, what’s stopping malicious actors from just creating another Lemmy instance of their own then targeting another community until you’re forced to close that one like you did with Lemmyshitpost.