In some countries like India, people just assume that everyone uses whatsapp. It's gotten to the point where whatsapp has become the definition of messaging (for most people).
I don't see how Whatsapp is outdated to the point where one would compare it to IE, but I'll say whatsapp is more like Google Chrome than IE.
That's the reality in most of the world nowadays. Latin America is exactly the same (including Brazil) and while traveling through Europe every single Airbnb communication with the hosts was made through WhatsApp... 8 years ago, I imagine it's even more massive now.
My last trip to the US a co-worker was really surprised I kept sending voice notes and I realized I haven't called my wife in at least my last 3 trips... But we communicate a lot. Async is way better than sync.