In my research I've read those sentiments many times, but I don't fully agree. MMS was a universal setup, you didn't have to download any app, you didn't have to get your friends/family to download the app and connect with you, etc. That's the power of iMessage, it's already built in. I get that Google is trying to do this with Google Messenger, they just seem to be failing miserably at it. RCS is a huge upgrade over stuff like Whatsapp if for the simple reason that it (ideally) it should already be installed and ready to go for every single Android phone sold.
I'm also aware of the benefits of encryption and RCS lack of it. I just want something simple to send videos of my kids, if I want encrypted I'll just use Signal. Sure RCS will be a beast controlled by Google and US carriers, but iMessages is controlled by Apple, and so is each respective messaging app out there. Sure encryption ideally shields you from them, but that's if you trust the company, its servers and its relationship with other entities who like backdoors. Plus when you say cost effective you are, of course, saying out side of the US. My text messaging is free and unlimited (although my data is probably much much worse than yours).