The problem with thinking that "the more cushion compression, the shorter the bank" is that when applied to banks that are hit softer when the OB is near the cushion, the "cushion compression rule" will lead to the conclusion that the soft bank will not bank short, yet because the OB will slide into the cushion--just like with the hard bank--they will both come up short.
The bottom line is if you know the real reasons for certain effects, then you can figure out what will happen in most situations, where faulty beliefs will lead you to make faulty conclusions when applied to different types of shots. I think that is the point Bob Jewett was trying to make.