[Yoda]

How many professional golfers set up with the right forearm on plane?

The truly On Plane Right Forearm demands a Body at or near Impact Fix. That condition results in the Hip Slide (Weight Shift) that tilts the Shoulder Turn Axis (the spine) and thus lowers the Right Shoulder. This results in a greater Bend in the Right Elbow than when the Right Shoulder is higher in its non-Impact condition.

Hence, most great players -- especially Swingers in their Standard Adjusted Address -- have a Right Forearm slightly higher at Address than at Impact.