Might be a little bit of both but nothing you said there contradicts the original point--opening up iMessage integration to arbitrary bluetooth connections is a bad idea. It blows open access to all your messages...who knows, maybe even the e2ee keys. Law enforcement would have a brand new frictionless way into all your messages
I don’t think Apple would ever expose the encryption keys to your messages. Nobody would want it anyway: why reimplement the protocol when you actually just want to send and receive messages? And I fail to see why it would be frictionless for law enforcement, as they’d need to have access to your device.