I get that you don't want to use Google Messages, but it is the only one (that I know of) that supports RCS messages. If your reason for not using Google Messages is privacy, it's not a worry. You are using an Android phone; Google already has your data if you have a Google account. I can understand the frustration, but it's easier to just use the one that Samsung recommends. Also, it will work more seamlessly with multiple devices if you have a tablet or book.
Really it is exactly because Google *doesn't* have your text messages (yet) that this is happening. As for RCS, it is about as useful as an umbrella under water.
Unlike the rest of Samsung's software (which ranges between meh and utterly terrible) their messaging app actually had some useful features others do not have. That said, there's no shortage of SMS apps in the store that are better than Google's spyware.
