Well, I'm sure it doesn't matter "that much". But I suspect left-handers prefer controlling the stick with their left hand if given the preference, and so it matters at least a little. And so the question is if we are talking about maximizing pilot potential, is this little bit enough for them to block left-handers from the ranks of J-20 pilots. Though I guess if in China left-handers are forcibly switched to being right-handers early on, then this is not an issue. Or is it? Anecdotally speaking, my sister is naturally left-handed and was forcibly switched by my father as a pre-schooler, but she states she has some instinctive urge to use her left hand with new tasks. I am naturally right-footed but forcibly switched myself to primarily using my left foot in 1st grade, for kickball of all things, but I still snowboard down the hill left foot forward, like a right-footed person would. I don't know if there's scientific evidence behind it, but I suspect natural handedness may be a permanent feature of a brain.