Earlier quoted context omitted.
Years ago 1998ish(?), there was a fight to open up chat applications AIM, ICQ, YIM, etc. We had to have 20 apps to chat with each other. Fast forward 20 years, and here we are again, FB Messenger, Kik, WhatsApp, Allo, Signal, Telegram, SMS, Slack, etc. At least this appears to be a "standard" that everyone can use again.
https://xkcd.com/927/ Relevant xkcd.
Whatsapp, Telegram, FB, iMessages are NOT standards. They're closed systems controlled by a single company.
XMPP is a standard from the days of ICQ, AIM, MSN, etc. Unfortunately it failed.
SMS is a standard for mobile phone text communications. It's too limited now.
RCS is the evolution of SMS.
I don't think RCS is a redundant standard, it's a necessary evolution of SMS. It's a standard for a decentralized system. I know Americans hate their carriers to the point they'd rather have everyone's data in a single SV company, but the solution is to fix your carriers. Not to give all your data to a company (Facebook) that had been proved to be less than trustable about it.