Linear,
I am a big fan of Dr. Marshall's ideas. However, in this case I tend to agree with you.
Every major leaguer that I have looked at does move their elbows behind the Acromial Plane to one degree or another and not every one injures themselves.
That's a fact.
The thing that seems to make the difference is whether you move the elbows both behind the Acromial Plane and above the shoulders.
Guys who "Scap Load" with their elbows low seem to have few shoulder problems (e.g Ryan, Seaver, and Clemens). Guys who "Scap Load" with their elbows high (e.g. at or above their shoulders) seem to have relatively more shoulder problems (e.g. Drysdale, Madritsch, and others).
Coach Chris