Are you guys serious? You don't see how a measurement of the horizontal direction of your swing plane through the Impact Zone is useful? Have you ever heard of TrackMan? The Swing Direction, in conjunction with Attack Angle and VSP creates the Clubhead Path at impact. That's a fairly important Impact Collision Condition. Lia, yes the shaft bends in a full power swing, so that the sweet spot is in-line with the axis of the butt-end of the shaft. A straight line...inclined...its called the Vertical Swing Plane Angle. The line I draw on the screen is the VSPA. But if the camera is positioned ON the VSPA AND looking parallel to the Target Line, then the line represents a 0* HSPA. I'm not just drawing the line anywhere. I know where to place the camera. I've compared my method with actual TrackMan measurements. I know what I'm doing. Jwat's got a HSP of about 10* there, minimum. With a resultant "true" path of about 8*. Way too much. Not possible to hit a straight shot on-target with sweet spot impact.
Those are FACTS. As I said, I only teach fact. Here are some more facts.
* Jwat exibits more Spine Axis Tilt in that video than great ball-strikers typically do with an iron.
* The vast majority of great ball-strikers do not have their head, at impact, behind where it began, using an iron.
* Increased Axis Tilt has a strong tendency to shift the Impact Plane rightward.
* Torso rotation on a Spine Axis which is less tilted will have a strong tendency to move the Impact Plane leftward. In which case, you could say that a shoulder turn which is closer to level will "tumble" the shaft over onto the intended Plane Direction nicely. There's more than one way to "tumble".
* This more level shoulder turn is the swing key that Tom Watson has recently revealed in his video and book as the "lightbulb" moment of his golfing life, which finally enabled him to eliminate what had been a tendency for an overly in-to-out Clubhead Path (rightward Plane Direction).
* Since the arms can swing independently from their ball-and-socket joints, the vertical angle of the shoulder turn plane does not force the arms and hands to swing on any particular plane direction. But it sure can have an influence. Jwat may feel free to simply swing the hands on a more leftward plane direction on the downswing, which will shift the sweet spot plane leftward, assuming that the sweetspot plane maintains the same relationship to the hand plane as present.
* For an on-line ball flight, assuming sweet spot impact, you must produce the required True Path and Clubface during impact. I have only focused on the Swing Direction/True Path component. The alignment of the clubface at impact to both the Target Line and the True Path, required for an on-line ball flight, varies with True Path. And it sure ain't the same for an 8* as it is for a 0* Path.
As always, these are not my "opinions".