That's all fine, but tangential to my complaint, which is about iMessage specifically. iMessage, as a system that strongly promotes e2ee as a core feature, should not be backing up its encryption keys to non-e2ee iCloud backup in any scenario. Messages should fall in the same category as keychain passwords and (yes!) Memoji, backups of which are always end-to-end encrypted even when ADP is not enabled.
In fact I would say calling iMessage an e2ee system is false advertising until this is corrected. Reasonable people would assume that an Apple system advertised as e2ee would make an effort to prevent Apple servers from having the keys to decrypt most iMessages, while the reality is with these defaults it's likely that a large majority of iMessages can be decrypted by Apple servers at will.
In fact I would say calling iMessage an e2ee system is false advertising until this is corrected. Reasonable people would assume that an Apple system advertised as e2ee would make an effort to prevent Apple servers from having the keys to decrypt most iMessages, while the reality is with these defaults it's likely that a large majority of iMessages can be decrypted by Apple servers at will.