Obviously, but the parent talks about Apple losing its US market to WhatsApp. Not sure that's remotely realistic, and them adding advertising only makes it even less realistic.
There was a recent interview (iirc maybe with Ben Thompson or at least he mentioned it) where Zuck said they were seeing their growth continue to accelerate in the US and it sounded like they’d be on track to overtake iMessage in a couple years if the rate continued.
Growth like that happens slowly and then quickly. I’m using WhatsApp more now and I didn’t use it before, so empirically I’ve seen the expansion personally.
This would not be true most places outside of the USA and maybe Canada. In a few countries/regions it might be a different third-party messaging app.