The system is protecting you against Apple employees, but not against law enforcement.
No matter how much layer of technology you put, at the end of the day, the US companies have to respect the law of the US.
The requests can be routed to specific investigation / debugging / beta nodes.
Just to turn-on a flag on specific users.
It's not like ultimate privacy, but at least it will prevent Apple engineers from snooping into private chatlogs.
(like some pervert at Gmail was stalking a little girl https://www.gawkerarchives.com/5637234/gcreep-google-enginee... , or Zuckerberg himself reading chatlogs https://www.vanityfair.com/news/2010/03/mark-zuckerberg-alle... )