IDK if the original hypothesis is true or not. But it's kind of impossible to make judgements on evolution based on anything we know about humans and society. Modern homo sapiens are only about 150,000 years old and were pretty sure any semblance of a modern hierarchical society didn't begin until about 7,500 years ago, much less the concept of money which only happened another thousands of years later.

10,000 years is a drop in the bucket evolutionarily, hell, 100,000 years doesn't even do much, so any theory of evolution or why a complex hormone like cortisol evolved to be used in the way it is now is way off base if you're referencing concepts like "rich" and "poor" or reference to any form of societal structure made in the last 10,000 years.