he is not a one punch ko power guy, no. but "out-cardio"ing isn't a very complete picture at all. yes he has cardio, but he beats guys with punches.
this article calls it "flat footed, volume punching style of attack."
When Nick Diaz fights...he's looking to press forward, trap his opponents in a corner and hooks to the head and body until his hand gets raised. With his opponents standing completely still and trapped against the fence Diaz doesn't need footwork, he doesn't need speed, and he doesn't need tons of defense....Trapped in a corner, Nick Diaz was able to hack apart Takanori Gomi, B.J. Penn, Paul Daley, Evangelista Santos, Frank Shamrock, Scott Smith and countless others with his flat footed, volume punching style of attack.
Frank Shamrock once said "his punches don't hurt, but after 100 of them you fall down". when asked why he fell down if they don't hurt, he replied with confused enthusiasm "I don't know!"
tough chin, good cardio, flat footed, punches in bunches. again, the article above explains it well.
"Nick Diaz is simply designed to fight the way he fights, and not many other fighters are."