Personally, I have more experience in wrestling (as my high school had an excellent wrestling program) than in MA. I do concede that the back of the head would be a poor choice of target against someone who actually knows what they are doing in wrestling (Personally, I'd suggest a shot to the clavicle--while prepared to sprawl).
Further, I'd concede that the majority of "Kung Fu" players (at least in the US) would be completely unable to compete physically with most BJJ or "MMA" style fighters. However, I'd attribute this to matters not dealing with the effectiveness of the techniques, but rather problems with the general culture of American Kung Fu students.
I believe few American Kung Fu students study it to be able to fight competitively. I mean, most people's exposure to "Kung Fu" or "TCMA" (really, pretend traditional arts) is in movies, where they see Wu Shu. So, Kung Fu is filled with people who want to learn flashy moves, and who play make believe that they can beat someone who actually trains hard, really hard, to FIGHT. As a result, you get people who don't train the grappling aspects of TCMA (Monkey style has some techniques in the forms I've learned that are mirror images of many wrestling techniques-- controlling the head with forearm, keeping the arms to the inside for control in a front grapple--etc). In China, you get a similar effect from the popularity of Wu Shu forms only training.
My only point is that there are some illusions created by ignorance of some of the rules in MMA which prevent an accurate presentation as to whether or not a certain style of fighting could work in a "real fight". BJJ and similar arts have an advantage in most MMA rule sets, because their rules for sparring are closer to the rules of an MMA contest.
It would be like taking a BJJ into a boxing match and claiming that boxing is a better art once the boxer won. The only difference is that there is an illusion of a lack of rules in the "cage".
At the end of any fight, a fighter who is better conditioned, has the best strength training, the best nutrition, and generally takes the fighting aspect of his art more seriously than his opponent would (more likely than not) win in a real fight,regardless of style. I'd bet that if you took someone who studied MMA/wrestling/BJJ, but only in an American Kung Fu style: two day a week, no conditioning, no competitive sparring, and put him up against a "top notch" western boxer, the boxer would win 10 out of 10 times. Would this mean that double leg takedowns don't work? Of course not.