In a simpler system yes. But they’ve developed a sophisticated system for syncing secrets called iCloud Keychain. Apple never knows your keychain. Once a new device joins your keychain circle it would in theory be able to sync backup keys and then restore, all without Apple ever knowing. They’re about to roll this out for iMessages which are also not readable by Apple. Backups are probably in the pipeline if they’re not doing it already.
Only if you have multiple devices... it would be nice if they supported this optionally (it would be nice if they supported any kind of end-to-end backup optionally).