Communities are for Lemmy and hashtags are for Mastodon.

They each make sense in their proper context.

My point is how could you ever count on deletion when the content is being federated?

Even if Lemmy devs made account deletion easy and cascade deletes your content, all it takes is one server run by an archivist and that content is never going away.

It seems inherently unfixable in a federated system, like trying to unsend an email.

Nothing is ever really deleted on the internet, especially if it was automatically replicated to dozens of other servers.