Not according to other forms. This is mostly the supposed western/olympic? form. I met Justin Ma (who translated the Gao Ying text), and asked him about this. You basically just don't try to rotate your arm at all, and have a natural, strong posture. Try to lean against a wall with your hand, and your arm extended, with your shoulder down such that it is effortless and stable. Arm not too bent but elbow not locked because that can lead to injury. So the bow elbow is in around a 45 degrees line for me as well, with no effort trying to twist it
Apparently the only reason western archers rotate their arm like that is to avoid archer's kiss (string slap on release), although a certain pdf claiming that olympic form was totally the best and most ergonomic said rotating it so the elbow points backwards (clockwise twist for right handed archer) is the way to do it and it increases strength somehow, with no explanation as to why.
Scott M. Rodell advocates the complete opposite of the western form: having the "cup" of the elbow point up and the elbow down, saying it also strengthens the joint. Thumb draw w/ arrow on thumb side (away from body) of the bow allows the bow to rotate outwards a bit so the risk of archer's kiss is reduced (in my experience as well as in a lot of other archers... most of us thumb drawing people don't even wear arm guards), so this can still work...
I've seen pictures and videos of archers shoot bows of 150+lb with all sorts of arm rotations.
Whether you get archer's kiss with that elbow position depends on your particular anatomy, whether you're "double jointed" etc.
I asked Mark, an English Warbow archer who's made records, about this exact same rotation issue:
http://markstretton.blogspot.com/2015/04/longbow-technique-why-does-your-bow-arm.htmlThe elbow and arm should be held in the natural alignment that is comfortable for you to push the bow as you draw. There must be a slight bend in your arm to allow for the string to clear and reduce string slap, but if your elbow is held either too high or too low, it will cause you injury. once you have found this natural line, you can then work on pushing the bow away from you with your bow hand, and drawing the string back with your other. If this is done correctly, then it will also reduce the possibility of injuring your back and shoulders.
My conclusion for now is that one can get used to any rotation of the arm with enough practice and stretching, but what's more important is that your shoulder is down, you're not hunched and everything is properly aligned. If you're not getting archer's kiss and your bow hand and both shoulders are aligned, just don't try to rotate the arm. I think you don't even necessarily have to have both shoulders and bow hand aligned? It's just easier to pull heavier weights with?
if the arm rotates a bit due to settling the bow shoulder, then that is fine. i think it's supposed to happen? But not the full 90 degrees
I've still been wondering about the perspective of someone with knowledge of anatomy.