whatsapp has fast caught up in features too - you can send and receive files/music clips/gifs etc. animoji/blue checkbox isn't enough of a differentiating factor to matter
The thing is - the cultural inertia of the USA is huge. American culture has a thing about not giving a flying f what the rest of the world is doing. In that sense, if nobody can defeat iMessage on American cultural ground, it makes it hard for the other messaging guys to look cool or legit. IMHO all message networks and social networks is built solely on inertia and I don’t think the inertia of any one region of the world can overcome that of the USA. Maybe if WhatsApp can take over the entire rest of the world - but China is lost already and so the war is already over.