Low Point And Left Shoulder Dynamics
 

Both the Low Point of the Stroke and the position of the Left Shoulder (Left Shoulder-to-Ball Radius) are established at Impact Fix (2-J-1). The geometry of the Stroke then demands that, absent special purposes, the Low Point remain fixed.

The Left Shoulder, however, is not fixed. Instead, it moves (from its Impact alignment) down and around its Axis (the spine). Having moved down during the Backstroke -- beginning, probably, with a return to Adjusted Address -- it must then move up on its return move to the Ball.

Meanwhile, both the Hands and the Clubhead proceed Down Plane to the bottom of their respective arcs (directly opposite the Left Shoulder).

Low Point Versus Both Arms Straight And Aiming The Thrust
 

Per 6-A-4, the Both Arms Straight position does not occur until the end of the Follow-Through (8-11). Until then -- well past Impact and Low Point -- the 'normal' position of the Arms prevails: The Left Arm is always straight and the Right Arm is always bent.

The bottom of the arc (of both the Clubhead and the Hands) occurs directly opposite the Left Shoulder. At this point, despite the fact that the Right Arm is still bent, the Club starts 'up and in' (1-L-15). Meanwhile, the Right Arm continues to Drive (via the Hitter's Muscular Thrust) or be Driven (via the Swinger's Centrifugal Force) toward the Plane Line (1-L-10) until it, too, becomes straight.

Regarding the Aiming Point, the fact that On Plane Thrust may be directed at a specific point on the Plane Line does not negate the Left Shoulder Center:

"Regardless of how the Lever Assembly is driven, it moves in a circle" (1-L-9).

Generation Of Angular Motion
 

Angular (circular) Motion is the product of two or more divergent forces and is thus a resultant motion. In the TGM Hitting model, the Mechancial Radius (the Left Arm and Club Lever Assembly) diverts Linear Force (Right Forearm Thrust) into a rotating motion. [An example of this action would be pushing a child on a playground swing.] In the Swinging Model, this rotation is induced by the turning of the Body. [An example of this action is an electric fan.] In either case, the rotation thus produced in the Golf Stroke is 'Down-and-Out' until Low Point and 'Up and In' thereafter.

The Down Plane Drive to Full Extension does not refer to the straightening of the Left Arm -- that Arm is already straight -- but to the Full Extension of the Right Arm. And that is why Thrust should be directed through the Aiming Point (and not just to it (10-20-A/B).

Re: Generation Of Angular Motion
 

Yes, and if that right arm (and right wrist) still has room to straighten - which it does - then the force generated can and does continue to move 'away from center' until both arms are straight - the maximum distance that the hands, and thus the lever assembly, can move until the nature of a circle forces them 'up' - around the circle.

Both arms straight is the key - driving, thrusting, or using CF to get there, you must get there. I fail to see why Homer chose to select the left shoulder as 'center'. That view is arbitrary IMO, whereas looking at the overall motion, the center of mass, the center of the 'circular force', the center of balance is IMO clearly the mid point between the shoulders in all good swings. The true 'radius' is a line from the center to PP#1 in 3 dimensional space. Force vectors, not body parts. A line perpendicular to the shoulder line, at both arms straight.

I appreciate you view this differently, and see that you apply your view 'very' well in your swing - a more stable left shoulder, weight left move which IMO limits only power (mass) potential - everything else being equal. The advantage clearly being consistency over a slight loss of power potential.