One can debate about whether it is relevant to control for things like income and see how predictive test scores are among students with similar incomes, minimizing the influence of test scores predicting who is high/low income. However, the first referenced set of studies for CUNY and Kentucky did not control for any of these variables, yet still found HSGPA alone was far more predictive of FYGPA than scores alone. Many others have come to similar conclusions.
In actual admissions at the colleges emphasized on these forums, it’s not a choice among only consider HSGPA in isolation, only consider SAT scores, or consider HSGPA + SAT and nothing else. Instead highly selective colleges often consider things like course rigor, HS context, essays, LORs, out of classroom achievements, how the above fits with planned major, etc. The more additional variables you consider, the more overlap the different criteria has with each other, making any one category add relatively little to the model. Test scores appear to be especially prone to this effect.