The Marines are different in a lot of respects. There are a lot of guys who just plain don't want jets and want skids or some other kind of helo as their first choice. That being said, they won't put you in Jet Advanced if you don't meet a minimum cutoff score that says you are at least better than average. There is no percentage as it varies from week to week and month to month, but for simplicity's sake, let's say about one fourth of USMC pilots fly jets and just a few of them will select the F-35. You don't join the Marines to only fly. You are a rifleman and an officer first. Believe it. I had seven Marine on-wings when I was an instructor in the Navy, and none of then selected jets (only a few of them even wanted them).