I think you're underestimating how much of the inequality has been baked in by Junior year of High School. 16 years of living a life where parents and teachers nurture the students for maximum growth is going to be easily reflected in any way you want to measure aptitude against someone that grew up in a rough environment.

From the article it seems like the UC are going to develop their own test, that will further divide those with resources that can study and prep for multiple tests and those that cannot.

The issues with the diversity in the UC system are rooted in a much deeper level of inequality in society that probably cannot be fixed with these band aids.