[Viscant]

A couple things.

Not to nitpick, but the best UFC champion is not the best mixed martial artist in the world. The best MMA fighter is unquestionably Fedor and he does not fight for the UFC and probably never will.

And also, Brazilian Jiu Jitsu has already been proven inferior to traditional Japanese martial arts...if you consider Sakuraba a traditional Japanese martial artist. He has destroyed almost the whole Gracie clan. Unfortunately, the best of them (Rickson) was never beaten so...it's not conclusive, but they don't call Sakuraba the Gracie hunter for nothing.
Regardless, BJJ has been proven over and over to be greatly superior to most other martial arts. The fact that Royce Gracie, really the runt of the clan, had such a great run is a great testament to this. The reason that pure BJJ no longer rules MMA is actually proof of how effective it is. I can think of no high level MMA fighter who doesn't have at least some BJJ background, at least an elementary defensive one. Even so called strikers in MMA train BJJ now. Tim Sylvia and Chuck Liddell are very loath to go to the ground but they have purple belts in BJJ. Wanderlei Silva is a black belt in BJJ. Anderson Silva has a black belt. Rich Franklin has a brown belt. All of these guys are thought of as strikers almost exclusively but they're all trained in BJJ now.

What makes MMA such an interesting sport is the fact that it's so new. In my first post on this thread I pointed out the traditional martial arts that many MMA champions started in. That's because MMA training (as exists today) didn't exist when they began their training. Because of all these different styles coming into MMA and their most effective techniques being assimilated and dissected, the advantages an MMA fighter has over a singularly trained martial artist keeps growing and growing. Even if the traditional martial art is the most useful, such as BJJ.
For example, how many MMA fights end by foot locks or heel hooks? Not nearly as many as there used to be. In the older days of jiujitsu, many masters refused to teach their students heel hooks, looking upon them as dishonorable and beneath them. Even today at some weaker schools, you'll see this mentality. Looking at the effectiveness of these techniques in the early days, now all the top schools teach these techniques and learn their counters and you see fewer people get caught.
This is just another example of how the sport is evolving past people who train in just one discipline or just in one way.

I believe that Sklansky limited the martial artist to "asian martial artist" primarily to exclude boxing, wrestling and brazilian jiu jitsu. These are 3 of the main pillars of modern martial arts. This is how I interpreted "asian martial artist" when I read the question. Such a fighter could utilize Muay Thai and crosstrain with judo, I suppose, however this style has already proven to be inferior (see also Karo Parisyian).