I too have AT&T and have experienced issues with their crappy messaging service. If you must stay on the stock messaging app, you could try turning off Advanced Messaging. I always had better luck with that off but it defeats the whole purpose of having such a feature. Their messaging is just complete garbage man. No way around it.
I switched to Google Messages a few months ago. They actually have implemented proper RCS and I had my wife download Google Messages as well. We quickly transfer high resolution messages and videos and still get read receipts and "someone is typing" visibility. I was amazed at how much better we can transfer pictures and videos with this service.
I was actually thinking about switching back to the stock messaging app to see if it had gotten better but given your thread here, I'll just hold off.
I know it's not an ideal solution but I would definitely recommend trying Google Messages. If you can get any friends or your wife or GF to switch too, you can enjoy true RCS the way it is supposed to work. Not AT&T's crappy, poor excuse for RCS called "Advanced Messaging."