what's the point of rcs when it's controlled by the carriers (aka you will be billed for it). at least with imessage it's free to send between apple devices.
On the other hand, I believe AT&T zero rates their RCS messages if you have an unlimited texting plan. (e.g. https://www.att.com/shop/wireless/features/advanced-messagin... > FAQ > how much does advanced messaging cost). Could not find details on TMobile except this article: https://newsroom.t-mobile.com/news-and-blogs/rcs-messaging-l...
But what if you don't have an unlimited texting plan? Let's say your current plan includes data + modest amounts of talk+text, but you do most of your communication over chat apps, so you never really touch your text allowance, even though you text a lot. now with RCS, you now have to pay extra $ for those texts you're sending out, or pay $ for the unlimited plan. plus with chat apps, you could send free over wifi. so from a customers point of view, RCS is worse in every way.