Overhand inverted punch - underused gem

One of the techniques I noticed frequently in the Rousey vs. Holm fight was the overhand inverted punch. In karate I suppose it would be an otoshi ura zuki (an inverted dropping punch). 1 Holm used it time and time again to devastating effect - both moving to the outside of Rousey's lead (something I'll examine in a moment), and sometimes just square down the middle on the inside, as shown in the three pictures to the right. However it lands, the technique is devastating. It's a very useful punch precisely because it is so unexpected . I suppose this raises the question why that would be the case. I'll get to that soon. But first, let us not forget what an oddity this technique really is - in both combat sports and traditional martial arts. In an industry often obsessed with rejecting any level of " corkscrew " in punches, it seems out of place to expect one that corkscrews to its maximum possible extent - ie. so much that the thumb ends up...