Yes, it defies logic that there isn’t an initial screen and that every application is “read” in its entirety. Why waste time on applicants that are obviously not academically qualified?
One data point in support: Dartmouth admissions used a numeric academic index, circa 1997. This was exposed by Michele Hernandez, an ex-AO at Dartmouth.
I agree that it’s remarkable that the inside scoop has not been revealed by more AOs that have worked at elite universities. The reason may be that they’d henceforth be pariahs in the admissions community.