About as many folks as I have encountered "on the street" who can throw a good solid punch.... I notice that there's often a big diff between a punch that freaking hurts or would knock someone the hell out vs a "correctly" done punch from a martial art. I also notice that a whole boatload of mma knockouts come from very unclean, very out-of-alignment, totally telegraphed but from an unexpected angle, unorthodox punches.
I only trained in kyokushin for half a a year, so my striking art experience is limited, but I think you're right. I also wonder about "correct martial art" punches. IME, some details are different from art to art. Particularly the use of the shoulder seems to differ. Also, some of the differences may be attributed to gloves (big / small / no gloves).