I can understand when people claim that Lesnar just "lays" on people because to the untrained eye, that's what it looks like, but in all fairness, that statement isn't accurate.
Lesnar's fight against Mir was like looking at a book of the different ways to destroy half guard. For example: Lesnar used the simple technique of pinning the head or throat of Mir with his mallet hand and moving his body back to prevent Mir getting under Lesnar's centre of gravity. Another was Lesnar using his own head on Mir's Chin and armpit.
One of the worst positions Mir was in, was when Lesnar immobilised Mir's left arm. Lesnar used his left arm to crank Mir's head forward while holding the arm-pit of Mir and simply feed him punches to the face.
Mir's worst position was when Lesnar had Mir up against the cage and Mir looked like he was improving his position from the half guard. Mir seemed to be getting to his knees until Lesnar controlled Mir's Left wrist, which in a sense trapped Mir against the cage and got pounded into a stoppage.
I'm not saying size wasn't a factor in the fight, but for people saying Lesnar "lays" on his opponents is simply not true. There was technique behind Lesnar's dominance and that's some of the technique he used.