bending at waist to match plane interrupts the desired sit/down/up action that is part of the more upright/adjustable swing.
As a "truth detector" look at clips:
IF bend at waist were the way to adjust, THEN guys would be WAY bent over for the inside low ball. They don't do this. Must be some reason.
reason is, the more you bend over(think of body/trunk as torsion bar), the more you get inefficient coil and uncoil becaseu rotation creates too much separation (more separation the more you bend over and try to "turn like heck from middle out") in the low parts of the chain away from the shoulders so that quickness and late adjustment are not possible.
Yeager explains well how weight shifts and the lead leg action is used to assist the body in efficient momentum transfer,discrediting the GURU's misguided/lack of understanding of weight shift/balance/momentum transfer that even a fancy name like "pelvic loading" or "vertical loading" can not hide.
Hope your defense gets you back in with the GURU, he needs you (believe it or not, you know more than he does).