alt Hacker NewsSMS is a defacto carrier tech that people expect to work, people also don't expect e2ee or any kind of privacy scheme on SMS but it might be a place to hand communication off to a different tech. Whereas RCS leaks meta data to the goog or worse (I don't know the ins and outs of RCS) but by default I would trust it less then signal, who may also collect meta data leaked through the goog, so I guess the real solution is to be boring and assume there is no security or privacy for anyone of reasonable means.
Signal > RCS > SMS.
Just because RCS can't be done without metadata doesn't mean it's a fruitless endeavor. Why not have someone use RCS to then get on Signal? That is so much better than plaintext SMS to Signal.
And for most people, RCS between Android <-> iOS is the biggest advancement in encrypted communication for the layman that I've seen since Let's Encrypt.