By definition, any really effective backup (off site, offline) can't simply be modified instantly when you click a button in a web UI. The reason it takes months for backups to clear out your deleted data is that's how long it takes for the entire backup to be discarded and replaced by a new backup that reflects your deletions.

While the data is likely inaccessible forever in this case, the reason the company can't just say it's been deleted is if they actually do need to restore one of these backups, the data you deleted will come back.

The only way in my mind to grant your wish would be if you owned the storage of your credentials. Otherwise you're just moving trust to another entity. I'm not an expert.

Either way that clause showed a hint accountability from Amazon that I haven't seen too often. Not that I've spent much time comparing ToS either.