Not exactly this. IMHO, theoretically from the biomechanical point of view, the most sound pattern would be a pattern that stays on the elbow plane all the motion. Even early Homer Kelley noticed it.
Since it is not possible to perform such a thing due to the fact how our elbow joints function, I claim that the longer a golfer can stay on the elbow plane with forearm perpendicular to the spine angle during downswing the bigger are chances for consistency in a in-to-in swing pattern.
Another question is why some golfers, even the great ones, are not able to use the early elbow plane pattern. And this is a question to you and, first of all, to Brian.
BTW, Lee Trevino of course uses the elbow plane during downswing. And, moreover, how greatly he does this...sort of beauty:
Historic Golf Photos | Trevino Swing Sequence 9600 golf pictures, golf photography.....
Cheers
P.S. Sorry for a sort of threadjack with this elbow plane, but I think it is important to discuss this aspect in this thread.