Some guys just don't bruise or swell visibly as easy as others (ie. bradley, clottey). But it doesn't mean Pac wasn't landing the more telling shots.
He absorbs the shots with his head. . . Seriously, his large cranial mass, coupled with his perfect isosceles triangle points on his head, allows him to be more resistant to facial damage. .
Lol, he was in a wheelchair post-fight because Pac hit him so hard, it caused him to do a stanky leg, and he torqued his ankle. . .
A better question would be if Tim didn't land anything meaningful, why was Manny's mouth busted up and bleeding halfway through the fight?
Bradley's skull has consumed most of his flesh. The stuff you perceive to be skin on his face is actually shell, which doesn't bruise or swell.