1. Requires data connection, either WiFi or mobile data. SMS does not.
2. On Android, it goes through Google Messages. I don't trust Google.
So, I replaced Messages with another SMS app that doesn't spy on me and disabled RCS. If I wanted to do rich messaging through data connection, I would use Signal or similar.
So, RCS is not a replacement for SMS. It's just another IM protocol. And we have enough of those.
As for others replying through RCS, that's a failure of the messaging app, should recognize that the counterpart is SMS and reply in SMS. It's an attempt to force RCS...
SMS is for fast short messaging between mobile users, and that is its killer feature, it's universal. Every mobile phone supports it.
Signal dropping SMS support makes no difference for me, never used it for SMS, I used Signal for the secure conversations. Two different methods of contact.
So, I replaced Messages with another SMS app that doesn't spy on me and disabled RCS. If I wanted to do rich messaging through data connection, I would use Signal or similar."
3rd party SMS apps use a Google provided API to send and receive SMS messages on an operating system provided by Google. I'm not sure how you think using a 3rd party SMS app would be protecting you if Google cared about spying on your messages.
RCS through Google Messages is end to end encrypted while SMS is not, so you haven't eliminated Google in theory spying on your messages but you have assured that your carrier, the recipients carrier and whomever controls the OS and app on the destination device can potentially spy on your messages.