You are asserting that there is a ceiling on the effect of education on income. Agreed, but only 2.7% of the population has doctorate level education, and there

You are asserting that there is a ceiling on the effect of education on income. Agreed, but only 2.7% of the population has doctorate level education, and there is regression-toward-the-mean as well (many high-attainment folks have kids who are stocking shelves).