i heard something similar about designing questions for maths exams -- about half the questions should be pretty basic, so students who have studied and have a basic grasp of the concepts should be able to get them right and pass the course. then the rest are harder, with e.g. one or two questions being more difficult extensions of what was covered in the course.

it sounds like the structure of the marine officer training camp avoids the problems some students have with poor "exam technique" - if you are given a fixed block of time to use to attempt all tasks (e.g. the obstacle course, the exercise room) then there is the risk of students spending all their time on the hardest task, and not leaving enough time to succeed at the other easier tasks.

edit: on another hand, you could argue that "a student's poor exam technique" could equally well be called "poorly designed exam / measurement process"