Not correct of heavier having edge everytime. you'd have to have a huge diff in weight for that statement to be true. A lighter arrow with a FOC in the 19% range can out penetrate a heavier shaft to a point. Also, my 391 gr out penetrate my 520 gr. FOC of 391's in about 18%. FOC of 520's is 11% or so. Weight forward helps penetration too. Also, lighter arrow traveling faster usually always has a higher KE at the same draw weight.

Of course, this stirs the same issue as The physics being fun post in here too.