Been-there insight and illumination by NavyHoops!
ACT performance is just one of a boatload (had to use it) of predictors for academic and overall viability at USNA, and more importantly, beyond. During my time as a USNA BattO, and from observing 20 years' worth of sponsor mids, I have seen exactly what Hoops noted: stellar-stats plebes who stumble and fall, and end up in the middle/bottom of the class, or separated, and more average incoming academic stat Joe/Janes who quickly adapt. Perhaps they have better time management and multi-tasking skills, and then flourish at or near the top of their class.
I particularly recall one mid who went on to medical school out of USNA whom I got to know through the interview process. I recall the profs at the USNA med school review board (I sat on the board as the Commandant's rep to evaluate professional aptitude) expressing their admiration for this mid. We had looked at his incoming admissions stats - regular quality HS, not the top SAT or ACT grades, but an overall well-rounded achiever. As a mid, he racked up an astonishing GPA and order of merit at USNA, did Honors Chem, with a language minor he used to volunteer during his summer leave blocks with Doctors Without Borders. Oh yes, captained a varsity team. Well-respected in his company. Won prizes at the Commissioning Week academic awards ceremony. I asked him after he had found out he was a Med Corps selectee how he felt, and he impressed me by saying he would forever be grateful to USNA for letting him in, because he knew he didn't have some of the HS stats of others, and he said he determined to work hard, ask for help when he needed it, and keep his priorities straight. He got a high MCAT score and had his pick of several top med schools.
I believe this is fairly common, that USNA is a place where many mids hit their stride and bloom. It is also a place where HS stellar-stats mids can soar as well as stumble. Handling the academics - with everything else going on in the SA pressure cooker - that's where USNA Admissions has to read past the stats, application facts, essays, interviews to find those who can succeed as a mid/cadet and go on to successful service as an officer, while meeting other goals for the class. A tall order. They make mistakes, but by and large over the years, bring in enough raw material to deliver the finished product in 4 years, with expected attrition along the way.
Best wishes to all who are facing a decision to accept, to those who are still waiting, to those who have been disappointed and must sally forth on a new path, and perhaps decide on re-application.
Filling out the class is indeed an art and a science, and as I read the posts from those who are disappointed or still waiting, I sympathize.