I just use Google Messages, but I'm signed out of the app. Actually, no Google acct on my whole phone. I stick to F-Droid for apps of I need em.
The way I see it, mousy sms stiff goes through the carrier servers I'd not Google, and at least Messages is RCS. However, I'm running XMPP and jmp.chat for a phone number to test out switching entirely and setting up friends and family on my server. Trying to go full hermit mode.