hmm my bad about UFC, in my mind all MMA is the same
dont watch it enough, it's indeed pride that's tough...
From my experience? Although 100% going at it standing up for a full minute is lethal, the first time i wrestled it completely killed me, the pure level of physical-ness of it completely surprised me...
That said, wrestling/grappling is so much a thinking game, if you know your stuff and play it smart, and know your techniques, you can make it a lot easier on yourself (once you're in a control point "all you have to do" (not at all easy ofcourse) is stay there and wear ur opponent out, or think of a way to hit him.
Standing up going at it like your life's depending on it wears you out insanely fast too, it's (to me) probably more intense than sprinting... although that might also be down to my stamina being alot less than when i still did track athletics...
Now, about the fighting classes: it is my feeling that most fights are determined on the ground too... Also, back in the beginning days of MMA, i believe most of the winners were grapplers who had enough strenth/speed to throw decent kicks and punches, and later the standing-up guys learned grappling techniques and things evened out (correct me if im wrong here)