Funny, you trust apple yet iMessage has major flaws that were written about years ago, that Apple has never addressed. https://news.ycombinator.com/item?id=38537444
And if you read the Beeper devs blog, you'd understand how much you misunderstand about the security and encryption implications. If anying, it increases message security by moving messaging from SMS to encrypted iMessage. https://jjtech.dev/reverse-engineering/imessage-explained/
He invited Apple to have a third party assess his work. So far Apple hasn't responded.
I have no issue with Apple blocking Beeper, it's their system. It's interesting to watch, but the DOJ has no reason to get involved here, it hasn't even been made a legal issue yet.
If Apple feels it's a legal issue, they could start legal proceedings. My question is why they haven't.