Man, I remember a few years ago when I was in a place without good Internet reception, but good enough phone reception. Wanted to send a SMS instead of a WhatsApp message and only noticed hours later that my phone switched to RCS without fallback and my "SMS" didn't go out because of the missing internet connection.

I disabled RCS that day and never enabled it again.

2G and 3G networks are dying. 4G+ is entirely packet based. "Phone reception without internet reception" simply isn't a thing once the final analogue networks die out. That's what RCS is built for.

RCS has the advantage of theoretically being able to get priority through the baseband, but if you're using Google's RCS servers rather than your carrier's, that's not going to work.