Brick walls have more inertia than the human head. The purpose of the punch is not to shatter the material (bone) but to wobble the brain causing a KO. I do agree that the palm heel is better for head strikes but that doesn't mean that you should discount the normal fist. (Historically the technique was there to make the punch without damaging the hand)

I agree with whoever said apply hard to soft and soft to hard. Use the right tool for the right job.