So iCloud Backup is not encrypted then?
However, I am really curious about whether or not using iCloud Backup negates these protections. For iMessages, Apple specifically says that it does: "If you have iCloud Backup turned on, your backup includes a copy of the key protecting your Messages." In other words, if you use iCloud Backup, Apple specifically holds a key allowing them to decrypt your messages in your iCloud backup.
Yes, you can never be sure that your landlord has not let other people into your house. Your landlord could let the police into your house
"Did you lock the house?"
"Yes"
"Good because I left secrets on the kitchen table"
"Oh, the landlord has a key. But it's locked"
"Um, ok. It's sort of locked. It's locked, but other people can get in. All I really care about is my secrets so I guess I'll just go back and get them and find someplace else to leave them that's more 'locked'"
In the same way a file can be encrypted, yet be insecure because somebody untrustworthy has the key to decrypt it. Doesn't change the fact that on a technical level, it's encrypted.
And how secure your landlord stores your front door key.
So if your landlord is careless and/or willing to open your door to people requesting them to do so, you can assume that your landlord IS indeed an adversary.
https://support.apple.com/en-ca/HT202303
EDIT: On a second reading it looks like there's a difference between the "on server" encrypted data and the "end to end" encrypted data. Backups are covered under the former but not the latter. Shame.
The fact people don't appreciate what Snowden leaked and infosec in general is as much a result of that as it is negligence or humans being 'bad'.