from what i've been reading, and based on my study of psychology - "aiming" whether split vision, gap etc - is a conscious calculation, whereas instinctive, is where you relax your conscious brain ( assuming good form has become a motor engram that it happens at an unconscious-competency level of function) and let your brain work out the "aiming Process". it's just a switch from conscious to unconscious method of getting the arrow to your target.
A good analogy in aiming would be likened unto Bowling - you consciously line up your arm going backward, then as it moves forward, you focus on it lining up with whichever arrow lines up the ball to the pins - where instinctive would be likened to throwing a baseball or football. you never look at the ball while it's in your hand, you don't focus on any gap etc. you simply look at the person, and the ball goes there.
In the end, it boils down to what kind of personality you have. some people like calculated, logically thought out processes, and I would say gap shooting or any other "aiming" style would fit them better. Me, I like listening to my body (even in the gym, I don't have a "routine", I do what feels natural). I like the feeling of trusting in the unknown, and getting great results.
hope I'm not beating a dead horse here