RCS is basically proprietary RCS.
It is not open, it is controlled by the telcos, and google has been pushing their own proprietary version of RCS to the telcos.
It’s no better than iMessage. This isn’t a problem in the rest of the world, they just all use WhatsApp.
This is a legacy of the US being out in front of adoption of SMS, and it still being ingrained. It’s largely only a US problem. And it’s not even really a problem.
I love iMessage, but I have WhatsApp and signal and like 19 other apps that offer messaging for people who prefer it.