It’s not worse than SMS in any fashion. Just like SMS, RCS will tell you when your text is actually delivered. You will never assume somebody received something that they didn’t. Furthermore RCS offers read receipt functionality which will additionally let you know your message was read. SMS is not capable of that.

RCS also lets you actually send media to your contacts, like photos and videos without horribly mangling them with compression.

And as for having no data connection, your phone will fall back to SMS same as iMessages do. Which shouldn’t be at all necessary as most people have unlimited data plans and even when throttled RCS has such a small footprint you shouldn’t have any trouble.