As one of the 'rare' FJ QFIs in the BFTS system in the 80s, I think there was a fairly clear nature/nurture divide but it did not divide cleanly around FJ/ME/RW lines! I can think of several streamed RW who were excellent aviators with bags of capacity but who were not comfortable with close formation or the high-dynamic events (as far is this was possible in a JP). Same for ME. There were also people still afloat in the FJ stream but who would probably be a training risk once they got to the SAP/weapons phase.
It was not until I did the CFS course, dragged kicking and screaming from the end of my first FJ tour, that I realised just how bad a few of my BFTS instructors had been. The penny should perhaps have dropped at Valley, when the (bona mate) QFI response to my first IP-tgt run was "What was that?!" followed by a question about whether I had been taught it by a Vulcan or a Victor pilot (= the latter) and then a demo of how it should actually be done.
My other conclusion about nature/nurture is that poor instruction can put a serious brake on talent that not all will be able to overcome. On the other side of that coin, good instruction can raise someone's game to the point where competence (but not brilliance) becomes possible. That comes back to the argument about putting the good students with the good instructors and letting the others sink or swim.