Some submissions are naturally brutal
By Sam Yang - Get similar updates here
I've grappled against 300lb wrestlers in the past. I've tried to armbar them from top, I couldn't. Imagine if you weigh 140 lbs but you're a high level grappler. Your opponent is 300 lbs but is a novice. Yet he can cling from a pull up bar with one hand nearly indefinitely. So that means he can grip 300 lbs in one hand for a long time. Now imagine two of those hands gripping together. Not only that but he can two hand curl well over a 150 lbs. Even with perfect technique, an armbar is essentially a back extension. Someone's back versus someone's arms, most of the time the back wins, but not always. Now imagine if I had tried to leg lock him? Or neck crank him? Basically attacking the strongest parts of him.
In lifting terms, most submissions use the same muscles as the deadlift. It becomes my max deadlift versus their max cling to exhaustion. My best shot would be to weasel my way to his back and choke him (attacking his arteries and not the neck), much like Rickson did against larger opponents.
Why neck and leg attacks can be so brutal is because they often require more weight, more strength, more speed, and a certain relentlessness. They're the limbs that are hardest to control.