1. You cannot opt to use SMS on Apple Messages when talking to someone. If they are registered on iMessage, you are forced to use it. This happens transparently, automatically, and for the most part, silently. This helps to create the illusion that Apple devices are just better at texting, and anything else is old and shitty. When in reality, Apple itself only supports their own proprietary messaging system, and an ancient texting protocol that is bad.
2. I hope you are right that RCS will solve everything once Apple implements it, but I don't have confidence it will. The biggest problem is how they handle group chats: If iMessage group chats cannot seamlessly convert into RCS group messages (without duplication or splitting) then it will solve it well enough. This is unlikely to happen unfortunately
You absolutely can disable iMessage for yourself and text anyone using regular texts (SMS) only, you are never forced into iMessage. You can deregister your phone number on Apple's website without any Apple device.
Also, where is the "illusion" about "being better at texting"? Apple is literally coloring the bubbles differently to tell you that _iMessage is not the same_. How much more explicit can it get?
2. I hope you are right that RCS will solve everything once Apple implements it, but I don't have confidence it will. The biggest problem is how they handle group chats: If iMessage group chats cannot seamlessly convert into RCS group messages (without duplication or splitting) then it will solve it well enough. This is unlikely to happen unfortunately