If that were true, RCS would have been implemented by carriers LONG ago like they were supposed to (the original spec was launched in 2008), well before imessage came out in 2011 and we wouldn't be having this conversation.
But you know who actually does have a TON of sway with Carriers? Apple. You know who probably could have actually gotten them to implement RCS? Apple. Apple could have solved the RCS dilemma even before Google decided to do things themselves.
Apple didn't even need to do much, just drop the mere hint that if carriers didn't start implementing RCS they might stop selling the iPhone through them and they would have bent over backwards to get it done.
They didn't because iMessage is just another tool to keep people locked into their ecosystem, and they've admitted as much. And any excuse of "Oh we wanted to work with the GSM consortium blah blah blah" is just that, an excuse for Apple fanboys like you to latch onto and parrot.