Several thoughts:
1. While the math ACT/SAT score is important, one of the most heavily weighted variables, it is not 1/3. Closer to 18-20% in recent whole person algorithms.
2. More critical and important than GPA, which reveals less information, is ranking among your peers. USNA takes the exact opposite (and far more credible, valid imo) approach from elitist, secular universities and LACs in counting ranking and standardized test scores as the more valid, credible measures of both historical achievement and aptitude for future success. And even the more intangible asset critical to success @ USNA and USN/USMC. Competitiveness.
They want to know how the candidate from Alaska and Alabama stack up. Both among their immediate peers and their potential future ones. While the ultimate validity of SAT/ACT examinations can be debated, for now, it's the only common denominator, even if it is dividing by zero.