Of course F-3 gives a shooting advantage, how could it not. In the MA you know if you are below your opponents line of sight. He will have no gun solution on you and you can slip his shot. However in the DA the guy using F-3 mode can make fantastic shots from out side his plane. Aiming has nothing to do with it. You simply use the planes out side view like you would a garden hose and spray tracers like water. Then adjust the stream until you hit the target, It ain't no mystery.
I bet 90% of the super shooters in the DA use it while pleading innocence if you call them on it. Most times they will be flying something with a lot of ammo like a P-47 or a perked cannon ride that don't need many hits to get a kill. I see a use in the TA for F-3 mode but not in the MA or DA. No F-3 in the MA would also have the effect of making it much harder to bomb tanks at a spawn in A-20s and other bombers with the F-3 option. I would like to see F-3 out of the DA & MA.