Note that he specifically wants CW to maximize his vertical GRF under the lead forefoot by P5 - P5.2 and he also wants CW to be pushing backwards (away from the target) and not to be solely pushing upwards. What is the ideological basis for that type of advice? I believe that part of it is derived from Kwon's opinions that a golfer should generate a large moment arm about the body's COM in the early downswing in order to generate a counterclockwise rotation of the upper body about the body's COM. However, Kwon has never shown how that counterclockwise force (operating in the frontal plane), which could cause the upper body to move away from the target, can actually generate more clubhead speed. I can certainly understand an opinion that it can help a pro golfer maintain his balance in the later downswing and early followthrough when releasing the club in a targetwards direction. JS takes this "idea" further and he wants CW to push upwards-and-backwards using the vertical GRF generated under his lead forefoot so that by impact the lead foot is unweighted and has a tendency to spin backwards away from the target and not only away from the ball-target line - which is a foot motional pattern often seen in reverse foot golfers, who are competing in long-drive competitions.

JS has further opinions that I think are non-scientific and irrational. At the 1:17 minute time point of the video, he infers that the lead wrist angle wants to let go (representing the release of PA#2) and JS infers that it will not happen efficiently if the lead foot is only pushing upwards, and not simultaneously pushing away from the target. JS claims that the lead shoulder socket must move backwards away from the target, and not solely move upwards, in order to release PA#2 efficiently. I disagree with JS, because I believe that the major "force" causing the release of the club (release of PA#2) is due to the efficient timing and the large magnitude of the centripetal component of the MoF that is due to the underlying biomechanical factors causing the lead hand's motion between P5.5 => P7.

Note that the torque causing rotation of the club changes direction at P5.5 so that the club is induced to rotate counterclockwise and the magnitude of that torque becomes increasingly positive in the later downswing. Note the direction of the black arrows - note how the black arrow becomes directed more centripetally (upwards) and it becomes greater in magnitude in the later downswing prior to impact. What causes that torque to be generated? It is due to the change in the hand arc path (hub path) where it is becomes directed more upwards, and not solely directed targetwards - and that is due to upward motion of the lead shoulder socket that happens between P5.5 => P7.

Here is Dustin Johnson's lead shoulder socket motion and hand arc path.