Note that (based on that article), you can disable iCloud Backup and leave Messages in the Cloud enabled, which results in your messages being backed up but the key to decrypting them not being backed up. IIRC, this also results in the key your device uses to decrypt your messages being regenerated so Apple can't go into your backups and pull it out.

I disable iCloud Backup because there isn't much that is useful in there that isn't under one of the other checkboxes (Photos is separate, Health is separate, Messages is separate), so my messages should be safe?