This is the problem OP. This is what everyone is trying to tell you - there is no “better strategy” for getting into highly selective programs. Your child needs to choose the high school program that he is most comfortable going to for its own sake. The point of high school is to learn and grow as a person. If you are forcing something, there wont be the same level of success.
As was stated repeatedly, if your son is aiming for the academies, stay in scouts and excel in athletics. He can do that at any school.
As an aside, I would take the school rating with a grain of salt for a brand new school with no track record. As for the low rating for the IB school, call and ask for a school profile. The school should be able to give you the % of students going to college, average test scores, where students are going to college, etc… You can get those stats for your local public school as well.
Lastly, tell your son not to rob himself of his childhood especially for a “dream” where even people with perfect stats and national awards are rejected yearly. Enjoy the high school years, they go by in the blink of an eye. A hard working student will get into a great college and there are many pathways to becoming an officer. Nearly all schools offer ROTC programs.