Google is making strides to make SMS/MMS as feature rich as iMessage, but on my end... Samsung is not following the lead.
I like using Samsung Messages over Google Messages when it comes to SMS apps and supposedly Samsung Messages has RCS built in. But unfortunately, me and a buddy of mine... are unable to experience RCS. He's using Samsung Messages as well.
I've been following Google with RCS and I'm aware they are constantly trying to improve on the service, however.... they fighting a uphill climb. Not only do they have to battle with carriers, but phone manufactures like Samsung as well.
If you use Samsung messages then you are going through the carrier RCS rather than Google. I know Samsung is supposed to merge to Google Chat soon, but I don't think it's widespread. If you both use Android Messages and their RCS, you shouldn't have any issues. Been using it for the past year with minimal problems.