Luke who after having flown the equivalent of a Piper Cub (Incom T-16) is suddenly able to fly an F-16 (Incom T-65 X-Wing) just like that.
The usual counterargument to this is that somewhere in the EU it's mentioned that the T-16 and T-65 X-Wing have similar controls, which is of course not mentioned anywhere on screen at all.
Rey might not be a Mary Sue, but clearly Peter David is an idiot.
Or maybe he's just ignoring the prequels which bump the total count to... let's see... four.