Ok, so you think that say some state schools it might work ok, but not at say Stanford or Harvard. What about say folding in AP exam scores?

Not every school has AP classes. In fact there's a direct correlation with AP classes existing in schools in neighborhoods where income is higher.

This is why MIT got rid of considering Subject II tests because even on top of already relatively wealthy select schools that offer AP classes only a select few of those offer classes that prep you for subject II test.

It's essentially exponentiating the amount of opportunities rich kids have to slice themselves within percents different from other rich kids at their school but overall entirely leaves behind students who weren't lucky enough to born in a neighborhood with a tax bracket that determines the schools funding.

If they're not gonna use tests as a measure, then it's probably gonna fall more on interviews / motivational letters / extracurricular activities.

Again, when you have so and so many perfect students, you need to use other features - otherwise you might as well draw random names out of a hat.

These schools (Ivy Leagues, Stanford, etc.) first and foremost want the students that are most likely to succeed at their schools. They know fully well that there are far more good students (on paper) than spots, but they also know that two 4.0 students are not alike. Some will fail, no mater how good they are in HS.