In my opinion it's unreasonable to think anything can truly be deleted in a federated system. Even if the official codebase is updated to do complete deletion & overwrite, it's impossible to prevent some bad actor from federating in a fork that just ignores deletion requests.
Seems sensible to just not post anything that you don't want to be available for the lifetime of the internet.
I don't expect my data to be fully deleted in a centralized system either. even if it was deleted from the central server someone might have made an archive of it
and reddit is definitely guilty of this since they were bringing back peoples deleted comments and accounts