Well, as long as you keep a "baseline" of having "real" flight model, damage model, and gunnery model, I don't see why you can't add as many other "realism" features as you want, but then make them "player-selectable."
For instance, say you added full engine/prop controls. If I elect to USE full engine/prop controls, then I would get a SMALL performance advantage, be it slightly increased range (i.e. different fuel modifier) or maybe a couple of percent more horsepower IF I set my engine/prop "correcly." If I DON'T use the full controls, then my engine/prop are set "permanently" at a "good" compromise setting, but I don't get quite as "optimum" performance as the guy who's doing all his own management. OTOH, the guy who uses full controls "poorly" would get less out of his powerplant than the guy who just uses the default "good" system. An "expert setting," which rewards you for learning it (but only a SMALL reward).
Other realism features could be toggled on or off, like the nav map, gun jams, etc. Using them would give you a slight score modifier, which could also be tied into the perk point system. Selecting the lower difficulty settings would be fine, but you'd have to get a FEW more kills to have the same score/points as someone on full difficulty.
And everyone stays in the same arena, so long as you don't compromise on the flight model baseline