awblain, how does a puff of wind apply a couple to the disc? Remember that the forces coming from the swash plate are being applied through 360 degrees of rotation, not just at one spot at 90 degrees.
For your theory to work, one blade receives an input ONLY at 90 degrees to the pilot's right, no more, no less, and that makes it precess down. Something pushes down on the tip of the blade for a poofteenth of a second, or pushes on the left side of the mast, and the disc tilts. Horsefeathers.
Precession and couples at 90 degrees are not the reason a rotor system behaves the way it does.