Earlier quoted context omitted.
I don't remember Hangouts being broken, but Google didn't keep their attempt to onboard people by making it the default SMS client going very long. To me, that seems like a major error on their part, though I think I'm glad Google didn't succeed in popularizing a proprietary unencrypted messaging service.
It would have been encrypted by now (at least for hangout to hangout chats) had it hung around. And at least it was cross platform but overall I agree that mobile messaging should be standardized and open. So while the Google messaging strategy has been an abject failure overall, they did eventually trip over themselves and stumble onto the right path.
Google's implementation of RCS isn't very standardized or open. So far, I believe it's only available with Google's client and Google's servers.