I just tried simulating shooting like that, turning my hand out, and it just ain't gonna happen for me. I can knock, and draw an arrow, in one move, without looking at it. I cringe every time I see a compound, or recurve shooter, hold the arrow, just below the fletch, and bring the arrow to the string. When I was a small boy, I used to be able to grab an arrow by the knock, and knock it in one smooth move. I think the whole compound thing has infected the recurve, and primitive set. I don't see how turning out your hand in an unnatural manner, could enable you to shoot faster, let alone pull a heavy bow back.
But if people are doing it, I guess it works for them. buuuuuut not for me.
Wayne