It's the same situation in Japan. I've lived here for 5 years and literally never, not once, sent or received a message to anyone else here in Japan using the iOS Messages app. LINE messenger penetration is 100%. You don't ask for someone's phone number, you ask for their LINE username. And if you want to call them you use LINE's voice calling feature (which uses data so doesn't cost you minutes). I don't have anyone's personal phone number aside from my wife. Even my elderly mother-in-law makes calls using LINE.
My iOS Messages app is just pages and pages of phone number verification and 2FA texts, and then one group chat with remote coworkers abroad.
Most people use sub-$200 handsets, so the penetration of iPhones is very low and only the high class uses them. Within small social circles (mostly within the family), they use iMessage. But to communicate with anyone else, they use WhatsApp. I know a few high powered lawyers. They use WhatsApp exclusively.
WhatsApp penetration in Mexico must be about 99% in my estimation.
