In my opinion the downward shaft angle you speak of is un-necessary and only a result of incorrect club movement and fundamentals. It is a product of the conventional "hang your arms below the shoulders"; hands lower than impact plane swings that so many people continue to use to play golf.
The downward shaft flex you talk about is minimal if not non existent with the single plane swing that I refer to. This is because the spine / shaft relationship is maintained. In other words, the bending of the shaft that you speak of is seen when the club moves from a lower plane to a higher plane.
This upward bending of the shaft is due to an upward movement of the handle when the club moves from a two plane to the proper spine / shaft relationship.
The larger the angle at address to impact, the more upward and downward bending of the shaft. I have seen this bending in the shaft from extreme amounts to practically none with Moe. (I say none because it is not visible using the footage I have of him).
I account for this angle by saying that you can minimize it and eliminate it if you match spine / shaft plane with address plane. - my definition of the single plane.
You said. ":Moe had an angle between the leading arm and club at impact with the hands more ahead of the ball then they were at address. This angle formed between the leading arm and clubshaft also make the distance between leading shoulder and clubhead shorter at impact then it was at address. How do you account for that? "
I don't quite understand your point here. What I think you are saying is that the lead shoulder is in the same position at address and impact and this is not the case. I am not saying that the body starts at address and impacts in the same place. I am only speaking of club design and the plane of the club. The body must move to move the club on plane and return the club to its intended design at impact.
I think that is what your as saying. Please clarify this point.