Edgar is not a soft puncher you don't understand boxing if you think that. Jake Shields is a soft puncher; Edgar is a solid puncher he delivers sharp accurate blows that will often stun his opponent. A good MMA comparison would be Martin Kampmann.
His cross is especially good and takes a lot of his opponents striking power away. Usually halfway through the second he will start planting when he throws his cross and straight which takes the strength out of his opponents legs. This is one of the reasons why he doesn't get hurt past the midway point of the fight usually. His opponents don't slow down just because of the pace but because of the number and sharpness of strikes he lands on them.