I didn't even know this happened. Mainly because the moment Google blocked rooted and custom ROMs for Google Messages. I just stopped using the app outright.
Man I just realised there's a Gemini button! I never actually open the app, I use shortcuts from notifications! Good on google letting users opt out of something basically no one wants!
I had already blocked and reported Gemini as spam in the hopes that it would hide the button (spoiler: it didn't)
If whoever is managing Messages let this go through, maybe it's a good sign for other apps potentially removing their forced AI chatbots from where they don't need to be!