Here's the thing; are those MMA guys tough? Good god, yes. You have to be tough as nails to even make it past the smokers, (club fights), and actually get any pro fight in the cage. All of these guys are trained in at least one or more martial art as Rod points out.
Thing is, there are a lot of tough guys out there. I had an uncle, (dad's older brother), who was just a murderer w his fists. When he was 16 years old, he was beating up tough guys in the roughest bars in the bad part of town, etc. This thread has me thinking about him.
When my dad died a couple years ago, we were cleaning out his house and going through old photo albums. My sister was looking for the photo of uncle Pat, we had all seen it as kids, of him fighting for the heavyweight title of the US Army in a boxing ring set up on an aircraft carrier in about 1951. Prob Korea, my dad and him were in the war. He lost but you have to imagine how tough he was @ 180 lbs making it to 2nd place.
I'm about his size and any of the guys he fought would have put me to sleep immediately, without a doubt.
Anyhow, he went on to live a great life and retired as a police Lieutenant and detective after 30 years of service in Minneapolis. I posted his obit 10 or 12 years ago here.
My point is that his ranking as a pro boxer at the time would not have been in the top 200, I'm guessing. But he would have knocked CM into next week. He would have taught him a lesson that he'd never remember.