What makes the turned over fist often superior to a vert fist, to me, is that it's a lot easier to protect yourself with the turned over fist. The shoulder seems to more naturally come up (or come up on its own) to protect that side of the jaw/face. Whereas with a vertical fist, the shoulder doesn't really come up for protection, and even if you purposely bring it up, it just feels unatural. At least that's how it comes off for me, from how I was taught the vert fist (which was to fire it off almost like a shovel hook, but with a straightening/lengthening of the arm).
I would guess that's not the case for everyone, and I'm not saying you're wrong - that's just my perspective on it, based off my training/what I've seen.