I was having issues with RCS and my newly minted and number transferred GrapheneOs phone. This pushed me to call a buddy who recently retired from working at the big Eastgate, WA campus. (if you know this campus you know which one of the big three I'm talking about) Pretty much he laughed at me and said, "since i retired and half my friends are overseas I use Signal."
It was the last project he worked. Google pushed it hard and rollout slipped big time. Fedup he retired.