I am quite sure that dragging action occurs but I don't claim to understand the anatomical/kinesiological process that makes it happen (or allows it to happen). As you know, Blake attributed the critical connecting element between thighs/hips and arms/club to be his unique extremely forward trail elbow position. As his concluding sentence in GTTB he wrote, "But don't forget--KEEP THAT RIGHT ELBOW WELL ACROSS the body. Otherwise, you are wasting your time." I have observed no other golfer who achieved a trail elbow position as far advanced of the trail hip as Mindy recommended. If true that no one else had discovered this phenomenon, then presumably no one else would have (intentionally) developed a swing based on the idea. Though anecdotal, my own experimentation suggests (to me) that he was right about the criticality of the connection. My most solid feeling ball contact occurs on swings in which my trail elbow is most forward.
As mentioned before, several well known golfers have described a dragging or pulling action as the first part of downswing but usually without a satisfactory explanation of how it happens. Among these are Ben Hogan, John Redman and Joe Dante. In two chapters ('Starting Down' and 'Through the Ball') of "Four Magic Moves" Dante made an intriguing and commendable effort to explain the process involved in the downswing. About the pulling action from the top Dante wrote:
"The whole downward action is initiated by the lateral movement of the hips to the left. Since at the top we are in a tightly coiled position, this hip action causes the shoulders to rock to the right and turn. The rocking action, with the left shoulder coming up and the right going down, is what moves the arms and the club...Keeping the head back helps the slight rocking action which brings the right shoulder down."
Dante emphasized that hips must be thrust laterally to the maximum extent possible prior to their turning. This description seems plausible but I can't verify its correctness. There was no mention of hips and arms/club operating in two different planes. Without that, would you say his explanation is thus rendered insufficient or, perhaps for other reasons, is wrong? Jim