Let's not jump the gun now, this fight goes in the clinch it's Randy's world. There's absolutely no way Brock will intercede with strength and size to counter Randy in that department, if the fight hits the canvas which I assume it will at some point.
While everyone's bringing up Randy's age and inactivity into the equation, Brock's size gives him negative connotations as well. I'm sure his conditioning is up to snuff, refining his tools at a great camp with marquee trainers around him constantly guiding him into the right direction. But that doesn't equate to superiority in cardio by any means.
You lost me a bit. If it goes to the ground, Brock will be ontop of Randy. If it gets to standing in the clinch, Brock will indeed use his strength/size/speed to take advantage of the situation.
Like I said before, if it were running laps Randys in good shape. Its an MMA match though, and Randy is going to be the one carrying all that extra weight of Brocks much of the time.