That's an interesting way to math it. Your calculation of the number of millionaires is high because some billionaires own hundreds of millions of dollars.

According to google there are approximately 46.8 million millionaires in the world. There will only be 21 million bitcoin.

Less than half of current millionaires could possibly own a whole one.

Plus, 4 million BTC (nearly 20% of total supply) are already thought to be lost forever.

There's definitely not a whole lot of them for something serving as the root of a worldwide movement / new financial system