The basic idea of the passive arm stuff on the forehand is that there should be no conscious moving of the arm. Instead, the body's rotation should essentially catapult the arm from the takeback position through contact.
here's a video explaining.
I just don't believe high level players don't control their swing path by having some conscious movement of the arm. I know they're very relaxed, but I don't believe the arm is completely passive.
I've seen Federer shadow swing and he kind of traced the swing path with his arm only. No torso rotation. That indicates to me that he does have some focus on his arm and is moving it somewhat consciously during the swing.
I'm very open minded, however. So, if you think I'm wrong, please chime in.