Fwiw I have never found a two/three pin airplane where one of the pins wasn't secretly a stereo pin anyways. Or maybe I was getting mono audio but I was definitely getting audio in both ears.

I actually have one of the cheaper knockoffs and I do see some delay but it was never particularly bad. Like it's about as bad as I expect these entertainment systems to be anyways even with wired headphones. I generally expect A/V sync to be terrible on most equipment. I think people are just used to it these days.