Seems like you're only thinking of one piece of the puzzle, which your Android phone sending RCS thanks to a carrier allowing you to. Doesn't address this part of the problem:
"Even if Google could magically roll out RCS everywhere, it's a poor standard to build a messaging platform on because it is dependent on a carrier phone bill. It's anti-Internet and can't natively work on webpages, PCs, smartwatches, and tablets, because those things don't have SIM cards. The carriers designed RCS, so RCS puts your carrier bill at the center of your online identity, even when free identification methods like email exist and work on more devices. Google is just promoting carrier lock-in as a solution to Apple lock-in."