I got to give JR a lot thanks for helping me with my form. It's sometimes hard to understand what he is saying, but it's all typically spot on. I agree the pre-swing helps maintain balance and finding the hit as well as clearing the body into the backswing and rhythm. Not sure I totally agree about pre-swing reducing accuracy because mine went up when I began incorporating it, although I also began to hit it. I tend to lose the hit and accuracy without the pre-swing. I equate the pre-swing to addressing the golf ball, it helps give you a destination to hit through.
This vid is actually maybe the best for understanding reachback and weightshift. Dion briefly talks about it in his distance vid shifting to the heel. The weight shift in the downswing happens from behind you and its only about 1" long. Most players try to shift their weight from in front and doing all the things Shawn Clement says in the vid below.
Going back to JR talking about the Brinster hop. I believe the Brinster hop is equivalent to Hogan's power move and centripetal pump. The second vid he talks about having a great access to hit through the ball...this is how I think of the power pocket. Brinster pivots/clears his body into the backswing and glides front foot/leg forward all while in the air/being weightless, and then uses the centripetal pump for serious rotational speed. You can still see the centripetal pump in all the top guys, its just magnified with Steve.

