Yeah, that's sort of why I like K/S after a # of sorties, because it's good for players who can't play all day, and its very hard to game it, especially in harder aircraft. Unfortunately K/S per plane per person would be hard to measure, and would have to go by the honor system...
I feel like K/D would be the best way to measure it, even though players would perceptionally fly timidly. Though I find it very difficult to fly timidly in harder slower planes that take more patients. It would still be challenging to score a hi K/D in harder planes.