Google is trying to kill open source based on the assumption that their code is good enough to stand on its own, but as we've seen before, the majority of innovation that occurs on Android and it's derivatives come from third party developers.
On my crdroid rom I use the Google official dialer and message app and they are pretty similar to the aosp one with more features. So I don't have any reason to go back to aosp apps maybe for privacy but, for privacy just throw the phone cause the system itself spying you.