The word “Presumably” is doing a lot of heavy lifting there. That Econ101 justification is harder and harder to keep up as you learn more about both economics and the real world.

For detailed counter arguments, see Branko Milanović Global inequality: A New Approach for the Age of Globalization, James Kwak Economism: Bad Economics and the Rise of Inequality, Walt Bogdanich & Michael Forsythe When McKinsey Comes to Town: The Hidden Influence of the World's Most Powerful Consulting Firm, and many other books.