your acting like it was one of the fastest paced fights out there, Plenty of fights have had a pace like that, the two of them looked like roy nelson after a 20 mile jog.
You are not getting it. Do a fighting based workout for 25 minutes, running, bags, pads, weights, grappling etc. 5 minute rounds, gets a sweat going but no problem.
Do that while a Shogun or Hendo punch you in the head, kick your ribs, kick your legs and take you down, I'll bet you don't complete the routine.
Shogun took minimal damage in the first Machida fight and looked ready to go again, that was 5 rounds. He took massive damage against Hendo so yes looked sluggish, but to control the latter half of the fight and keep attacking as he did... Requires fitness.
MMA is becoming home to more and more gifted athletes, and the requirement for fitness grows all the time. Nobody is going to look athletic in a fight like that though. The lighter weights do, but their dealing with much less firepower.