>has always been able to read encrypted iMessage messages
...assuming you have icloud backups enabled, which is... totally expected? What's next, complaining about bitlocker being backdoored because microsoft can read your onedrive files?
Absolutly, they intentionally make stuff sound secure and private while keeping full access.
If you read the link you would know that contrary to your expectation other apps advertising E2EE such as Google's Messages app don't allow the app maker to read your messages from your backups. And turning off backups doesn't help when everyone else has them enabled. Apple doesn't respect your backup settings on other people's accounts. Again, other apps address this problem in various ways, but not iMessage.