Almost 80 million users of whatsapp in the US (330m pop) vs 120 million users in all of Europe (746m pop) kind of undermines that line of reasoning? If anything, the US uses whatsapp way more than Europe.

If we were looking at true third party messaging platforms that aren't owned by trillion dollar mega corps that can push their products onto every phone, then... maybe? The US barely uses Telegram compared to Europe, and signal's website sees about as much use from the US as it does from only Germany. But if the argument is about the US using iMessage more because they don't use other messaging platforms, then no, the numbers do not bear that out at all.