That’s why it works so well. What you see as problems with SMS I see as good design decisions. It’s an incredibly simple implementation that does exactly what it’s supposed to. You just want it to do more than it needs to.
Something will eventually replace it, but it sure as hell won’t be RCS. RCS is a defacto google standard now. Many features are locked out if you don’t use google servers. It’s not an open standard and it’s disingenuous to portray it as one.