Yes I know surprisingly large amounts about SMS.
Yes I know surprisingly large amounts about RCS too.
I suggest you go and read about downgrade attacks. If you compare iMessage/WhatsApp to RCS there's a big difference between e2ee being required and supported respectively. The only security decision which is tenable is secure-by-default and in RCS context that's only currently provided by Google's non-standard RCS extensions which are not universally supported by all clients.
You basically didn't say anything to be honest.
Also I hope you do know "Google's RCS" is standard on Android so basically you do get secure-by-default with RCS on Android.
Apple if they really cared about security so much could easily work with Google and make the RCS "secure-by-default" thing platform agnostic.
Anyway this issue is a technical issue which is conflated conveniently with a political one. The political issue is hiding the technical issue and the technical issue is that RCS is a **** show.
Again you didn't say anything, you just hate on RCS for the sake of hating on RCS.
The best technical solution is to use WhatsApp / Signal / iMessage / Telegram and ignore the politics. Politicians have no business in security - they just screw things up for everyone.
Realistically I use both 3rd party messaging apps and RCS. There's no conflict between the 2 anyway. RCS is a replacement for SMS.