Here in EU 95% of people uses whatsapp because it was released before imessage and not everybody likes iPhones, also because it's cross-platform. Never had any complains about whatsapp.
Somewhere near 95% may have whatsapp on their phones and use it to an extent, although many only a small amount, but I very much doubt its used exclusively by that many people with iMessage off and ignored. As above i use it for a couple of group chats but the majority of my messaging is done via iMessage.
I suppose its useful for folk if they have wifi but not a mobile signal or a very poor one. Some networks dont always allow the Wifi calling option that allows wifi to enhance the poor signal for phone calls etc so you can use audio only facetime to make the call over wifi instead.
It's only ignored because in the EU APPLE is not as dominant as in the US here the marked share is divided between more brands. Apple is about 25% market share (you can check official stats). So people use extensively whatsapp because it's cross platform and was the first free messaging app as nobody uses SMS anymore. Even people who have iPhones use whatsapp instead of iMessage.
I'm in the EU and barely use Whatsapp....there was a similar thread that talked about this and the claim that no one uses iMessage in the EU and we all use Whatsapp was pretty much made out to be nonsense. Yes people will use Whatsapp as well but not instead of in the numbers you say.
That's an official stat, actually published in 9to5mac 05 Nov 18, you can see in germany for instance ios market share 16% whereas android 83%, Spain android 92% iOS 7%
