I got so angry that I turned off RCS on my iPhone after I was somewhere with limited service, I was sending messages and they were being seriously delayed. Friends were trying to reach me and the same was happening. I finally broke down and got out of the group chat I was in and messaged the friend in the group chat that had iMessage and things worked great (still spotty but at least I did not think that things were working when they were not).

I don't know or frankly care where the problem is but it has made me swear off RCS completely. iMessage works and SMS gets the job done when I can't use iMessage.

I know why Google is pushing RCS so hard, but that alone should be concerning.