Weir does not set up as with the left forearm in line with the shaft. At impact it is inline. Does he not have to make some sort of club face manipulation to be correct at impact?
It is Axis Tilt (accomplished with Hip Slide in the Start Down) -- not Clubface Manipulation -- that brings the 'Trail' Shoulder down and On Plane. In turn, it is this On Plane Trail Shoulder that gives the player sufficient 'Trail' Arm, i.e., Elbow Bend, to manifest an On Plane Trail Forearm at Impact. So, for the Trail Arm to be On Plane at Address, there must be Axis Tilt. In his book, Power Golf,Ben Hogan had this to say:
"At the address there is no straightening of the right elbow. In order that the right arm will be limp and the right elbow down, one must list slightly from the right side. By list I meant that the right shoulder must be dropped and the hips faced slightly to the left."
We are saying the same thing: In order that there be sufficient Elbow Bend for an On Plane Trail Forearm, the Shoulder must be down and back (On Plane). And that is a function of the Hip Turn (assuming a Slide and its Weight Shift). That is why you see all good players with their trail Forearms On Plane through Impact, even though those same Forearms may not have been On Plane at Address.
By the way, isn't is nice that we have a TGM language where everybody understands that Right Forearm means 'trail' Forearm?