Does this matter to them though? Does apple care about having the dominant messaging platform if it's no longer a hook to get people to buy apple devices.
The US is one country, and what happens there is not representative of the rest of the world.
We were using whatsapp before iPhone even came to my home country, and living in Ireland now, everyone seems to be using it here as well. In fact, I'll venture as far as saying /not/ having WhatsApp is considered weird and you will no doubt exclude yourself from a lot of spcial circles.
A big part of Apple's appeal outside of tech circles is exclusivity. When people talk about premium whatever, more often than not it just means "what the plebs don't have". From that perspective, performative exclusion of oneself from some circles can be seen as a feature and not a bug. Nor is this US-specific - iPhone is even more of a luxury status symbol in much of Asia.
It’s representative of where most Apple software and hardware is designed and where their customers have atypically high disposable income compared to most other countries. They’re obviously doing pretty well with this strategy.
They aren't the dominant platform regardless of qualifier. Android has a 70% global market share. They aren't even the dominant platform in any country, barely breaking 50% in a few.
What's next, are we going to call OSX the dominant OS platform lol
First of all, it's simply completely unaffordable in developing countries so you can't realistically consider them part of the market. In rural India, an iPhone 15 pro Max or whatever is more than a year of income for many.
Coming to countries like the us, studies show that among younger folks, apple's market share is close to 90% [1]
The legal jargon surrounding what dominance is remains completely irrelevant, just like the legal system itself -- the punishments are pocket money for these companies, so it's mostly ceremony to keep lawyers employed.
But from a logical standpoint, they most certainly already are in many segments, and are coming to be in other segments.
https://www.wsj.com/tech/personal-tech/why-teens-hate-androi...