RCS is an open standard that Apple now uses as well.
I think there's a legitimate concern about having essentially two phone platforms, and how anything can really be "open" in that environment. But it's definitely a step forward.
And Google has built proprietary things on top of the standard, which is indeed concerning.
"Open" is an overstatement when it comes to RCS. You can't go out and write a new RCS client for Android, and you can't provide RCS on a new platform (or even unGoogled Android). It's open to the extent that both Google and Apple can use it; other major hardware vendors and carriers could, but don't (Samsung used to, and dropped it earlier this year).
I think there's a legitimate concern about having essentially two phone platforms, and how anything can really be "open" in that environment. But it's definitely a step forward.
And Google has built proprietary things on top of the standard, which is indeed concerning.