> I find it very dubious that the "Income Inequality" sits at the very first section, and "Supply-and-demand" at the eighth. I'm no established economist, but my understanding is you start at the foundational idea then move on to the its ramifications and symptoms.

Descriptive facts (like inequality) are more fundamental than the predictive theoretical models derived from facts (like supply and demand).

OTOH, it's true that social sciences often reverse these, both in pedagogy and in priority (and economics may be the worst of the social sciences in this regard.)