Let’s consider the two parts separately:
Re academics: USNA wants you to take the hardest classes your school has to offer — especially in STEM and English — and excel at them. They’ll look beyond your GPA, closely examining your transcript in the context of your school profile.
Re leadership: You get credit for holding certain leadership positions. But frankly, that’s almost a minimal expectation. What’s more critical is that you demonstrate “leadership impact.” That is, you didn’t simply hold a title but actually impacted the organization in a way that left it better than you found it.
The best candidates have strong credentials on both fronts. So back to the core question: Should you focus on academics or leadership? The answer is YES.
(Cross-posted with
@Heatherg21. She nails it!)