We can speculate for the exact calculations that were made by the Torah leadership in the US two generations ago, but the decision was made to have high school studies.
Specifically, in Telshe, the entering ninth graders were told to strive for making A’s by the Rosh Yeshiva (as I have been told).
For any Yeshiva bochur to neglect his secular studies program in his own Yeshiva is to be Porek Ol (discarding responsibility).