Oh, I'm pretty sure that if an army of guinea pigs would play this game, a handful of them would be stubborn enough to develop the muscle memory and learn to reliably hit their targets. I don't see a hard limitation on skill building here. The question rather is: How big must this army initially be to yield at least one sharpshooter? It's more about the steepness of the learning curve (no pun intended). People can develop intuition for the most complex things (I'm looking at disciplines like acrobatic archery for example).
I went a little bit on a tangent with the stereoscopic vision and depth perception, which might have been misleading discussion-wise. Sorry for that. My whole point there was: "You can't rely on information from depth perception (due to inaccuracy or complete lack thereof), which makes things more difficult."
Regarding proof: I can just speak my mind and utter some assumptions based on individual observation. If there's empirical data from a set of playtests that contradict my statements on certain points, I'm most likely the less reliable source ;)
Thank you, too. It was an interesting conversation.