> You also seem to be forgetting the most-populous country in the world – no WhatsApp there either.
However in the 4th largest (Indonesia) everybody uses WhatsApp (at least a few years back) as Facebook offered free data to their services there (internet.org / "Free Basics") whereas iMessage would cost money for data traffic or SMS/MMS.
Thus really different across countries and regions and social circles.
Same for the 5th, Brazil. Everyone uses WhatsApp here and has been more than a decade since the last time I've ever had to use sms (never even used mms).
You also seem to be forgetting the most-populous country in the world – no WhatsApp there either.
Between China and the US, that's already 20% of the global population unlikely to be using WhatsApp for most of their messaging.