Earlier quoted context omitted.
Do you really think someone's ending point as an adult is largely limited to their "brains"? Like, how are you going to completely exclude the upbringing environment and the scarcity and struggle for resources that some folks face.
It's not "what I think", it's what we know. One of the most well established facts in sociology is that IQ is the best predictor for life success: Firkowska-Mankiewicz, Anna, and Jerzyna Słomczyńska. Intelligence (IQ) as a Predictor of Life Success. https://www.jstor.org/stable/20628656 You reiterate my question in the second sentence: How do we weight these different privileges?
It’s the best individual predictor when compared against other predictors, but not very predictive on its own.
I.e. Iq is more predictive than inherited wealth, but iq + inherited wealth is more predictive than either individual factor.