..your assuming I give more weight to the concept than I actually do N. As if its a all conciously thought about in the end. The parts obviously have to have a musical independence so can't be physically linked so dependantly.
I can see that there is desire to let go in the end. however, the more consciously you programme something into your habit, the less easy it is to eliminate it in a final product. While I see value in the slow extreme rotation, I would expect any student to overdo it in the final product if I left them to just feel it after. I'd first give the antidote- by first getting them to practise only going up and down the three harmonic notes in a single fluid lateral arm gesture, with the keys being moved by the fingers. then I'd get them to strive consciously for the same fluid motion when putting the other notes back, without being tempted to reverse the arm direction on the way, simply because of the added details. I'd personally expect the final product to involve excessive complexity unless there's a step where you take the time to deliberately integrate the notes into the smoothest and simplest arm path, before going onto pure feel. the right hand makes it extremely difficult for the left hand not to get held up by desire to echo what the right is doing, which I feel makes it important to consciously perceive the continuity of action before just trusting anything- especially if the preparatory work was not based on a bigger unified movement but on constant deliberate changes of direction.
"As dima mentioned the rotation isn't a playing motion its a supportive one.. there is an angle of rotation that changes with every note, its extremely subtle in most circumstances.. if you don't do it you will over exert the fingers.."
I really don't agree it's so simple and definitive. too much individual rotation focus can actively strain the forearm unless there's a follow up of integrating all those constant reversals of direction into a more global and slow arm action- that may involve slow rotation through many notes but which may involve none. I once had an interesting lesson with Alan Fraser where he showed me how in bach's d major Prelude, the arm best moves laterally between 1 and 5. Interestingly, this actively moves in the OPPOSITE direction to that in which most the shorter notes are going. when you organise such movements well,there's no need to actively rotate a jot in the end product. you just need rotation as an initial exercise to learn freedom and good alignment to each finger. afterwards, the lateral arm movements are actually a much less effortful approach than trying to actively engage in constant reversals of direction. The example you give is a classic example for me of one where you need to think globally- not in terms of reversing the arm for a mere detail in the line. no active rotation is needed into C flat (going back down) as long as you have freedom. to get it light an unobtrusive, I'd actually be rotating AWAY from the finger, if anything. I don't believe taubman makes a single mention of this style of rotation - where it lightens rather than puts arm pressure through the finger.
"at speed, when you get rotation right, there is an obvious sense of support that feels very similar to parts of the slowed down version.. I can very easily "switch it off" and feel a distinct lack of support, and it's definitely related to rotational movements. Whether or not its actually "double" rotation is debatable. "
why not just to call it what it is- ie a singular slow rotation that involves many notes played via finger movement, during a slow simple movement that doesn't involve the strain of rapid reversals of direction? it's the fact that they cannot make this simple clarification between what happens in preparation and what you build up to really doing, that baffles me so much about them.