Rob: Unfortunately, you're making it sound, or you're assuming, that the process is: or can be: a lot simpler than it's being explained. It is some much more complicated, that explaining it in a paragraph or two is not practical. But let me address a couple of issues in the "Process".
1. Appointments are not just broken into categories of race, sex, or other demographic. The demographic also includes, "BY LAW", representation by state. All states' citizens pay taxes to fund the academy and military. That is why approximately 1/2 of a class receiving appointments, will be getting appointments from representative and senator nominations. So that all states are equally represented. Does that mean that an appointee from Arizona may be "Less Qualified" than a Non-appointee from California? Yes it does. But part of the reason for this law is to ensure equal representation. Not all the appointees happen to come from California, Texas, Florida, etc... because that is where the majority of the population lives, and it's such a small selection. 14-17% of applications.
2. The academies have decades upon decades of experience in what the applications look like. They want the whole person concept. Academics, physically fit, medically.... BUT, they also want leadership, team work experience, volunteer time, club and organization involvement, etc... I have personally had individuals who were physically and medically qualified, with a 4.0gpa and 31+ACT type academics, who DIDN'T receive an appointment. They did however get accepted to Yale, Brown, Penn, and other high end schools. Basically, they were all academic and nothing else. The military doesn't want this type of person. Unfortunately, many people think that if you are an "A" student, and can pass a medical physical and are physically fit, then you are 3Q (Triple Qualified) and should be a shoe in. Well, there's a lot more to being a cadet and military officer than your grades.
3. The military/academy's experience also shows over time, that the diversity they are looking for, goes beyond the "Old School" mentality that revolved around "Affirmative Action" and race/sex based filling of slots. Just like the academy looks at the "Whole Person" concept, that is what they are also looking for beyond the academy, in the "Real Military". They want their officers and military members to have a well rounded environment involved with working, living, teams, etc... made up of the same environment that our country is made up of. The diversity they choose from is NOT JUST RACE and SEX. It is poverty. It's single parent upbringing. It's the individual who demonstrates the OBVIOUS POTENTIAL to be the 4.0gpa student, but because they also worked 40+ hours a week, they have a 3.6gpa. But their ACT/SAT and other indicators demonstrate that given similar opportunity, they'd have excelled. It includes overcoming other major obstacles such as being 1st generation American. 1st person in their family who is attempting to attend a post high school education; and they had no support or role models motivating them. Point is: The military wants a well rounded military officer. One that can use their experiences with their past and the backgrounds of their peers, classmates, etc... that they've worked with, to make them better managers, supervisors, commanders, etc... when dealing with the diverse individuals with unique background. Again, it's NOT JUST RACE and SEX. This well rounded individual is developed through their experiences with others who have different backgrounds and experiences.
4. Finally; with the prep-school; these are individuals that generally have a single area that is not on par with their other areas. Maybe they are a 4.0gpa, sports, teams, etc... but they have a 20 ACT. "Maybe they simply suck at standardized tests". Maybe it's the enlisted person who's been out of high school for a few years and WON'T MAKE IT academically going straight to the academy. The academy requests "School profiles" from ALL APPLICANTS. Maybe a pre-school selectee is someone who's HS school profile shows LESS than 10% of each graduating class attending college, and demonstrates that their education system at that school sucks, and maybe this individual's 3.4gpa and 25ACT has demonstrated the potential (Based on interviews, recommendations from teachers, etc...) that they would have been a 4.0 at such and such a school.
In other words: The prep-school and the academy selections and appointments are not as simple as "RANK EVERYONE AND SELECT THE TOP 1400 APPLICANTS". That's not possible. How do you hard-score leadership, sports, team involvement, volunteering, etc... How do you compare directly the student who took 3 AP classes each year, to the person who was in the IB program and took ALL Upper level classes, to the person who had NO AP or IB classes available at their school. In their quest for "REAL DIVERSITY" (Beyond race/sex), how do you gauge or compare the 1st generation American applicant, who works 40+ hours a week, helping to support his single mother and 3 brothers/sisters, while taking grandma to dialysis once a weak, etc... and their 3.70gpa with the applicant who has a traditional family life, summer job at the pool/beach, who's involved with Meals on Wheels, is captain of the football team or drum major in the marching band, is also class president/secretary/etc...???
You can't simply take all those who are physically and medically qualified; and rank them academically by their gpa and ACT/SAT scores; and pick the first 1400 applicants. The military doesn't want just academics; and comparing academics from 50 states and thousands of school districts isn't that clear cut. Sorry, if you think it IS as simple as you believe it to be, but it isn't. And sorry if you believe that the only demographics involved is race and sex. There's so much more to it. Including the 1st half of the class being allocated to Congressional/State nominees, to ensure equal representation among the nation's citizens.