I don't use Google messages, I use an app called Textra, the network I use don't support it RCS and to be honest I really don't feel it is any advantage to me.
i also just don't like google messages.
There is no advantage to end users.
Only Google and Microsoft stand to gain from RCS since they're the ones who failed to build successful instant messaging platforms on the internet that people actually want to use.
It's a solution not for real people problems but for corporation problems.
RCS has been around for six years or more and it's still stuck in obscurity. My experience with technology that has failed to take off in six years is that it'll never take off.
Communication now happens via SMS/MMS if it's local. iMessage between iPhone users with unlimited (high cap) data plans. WhatsApp in some markets and between people from different countries, and to a smaller extent, Facebook Messenger.
There is no need for RCS in there. Few carriers support RCS and even fewer SMS apps support it (Apple certainly doesn't and if it can't run on an iPhone it basically doesn't exist in the wealthy world).