[Daryl]

Are they really on the elbow plane or appearing to be so because they drop their heads/torso (Tiger) on the downswing?

Whether it's an Elbow Plane or Turned Shoulder Plane, we're always talking about the Clubshaft angle. The following Image of Ben Hogan indicates that the Clubshaft angle at Impact points to the location on his side where his right elbow would touch.





So, regardless bobbing or swaying, it's the clubshaft that defines the plane.