Google’s protocol is proprietary too - their encryption extension makes it inaccessible for anyone else and google will not partner or license (companies have tried).
RCS as currently implemented is iMessage but with a coat of google paint. There is no there there.
Google should get plenty of shit too for closing down GTalk in the first place. It's not an either-or. Big tech in general hates open protocols and interoperability for consumer stuff; Apple is just the most egregious offender there.
RCS as currently implemented is iMessage but with a coat of google paint. There is no there there.