Earlier quoted context omitted.
What dwarfs iMessage in the US? I would assume that it is the most used messaging platform in the country.
Facebook Messenger - approx 140 million users, then WhatsApp at approx 75 million. iOS has approx 136 million users (not sure if that includes iPad). So "dwarfs" might be a bit extreme. However, its extremely unlikely that all the iOS users use iMessage and none use either Facebook or WhatsApp. Statista has the figures, but I'm not going to pay $149 per month to find out more! Source: Googling around, so take it for…
I would also guess it does more volume then FB Messenger, even if it technically has less users.