His ground game isn't awful. Having a guy like Lesnar on top of you and pounding you can mess up anyone's ground game. Don't forget, Brock smashed frank mir on the ground and we all know his ground game is legit.
I love jiu jitsu. Even more than I love mma. However, a guy the size of Brock, with that sort of wrestling ability, stength, and decent (blue belt) skills in bjj more or less makes him a high level black belt once he gets on top of you and is punching you.
Anyone who trains bjj knows what I'm talking about. When you are rolling with lower level belts, but they have amateur wrestling backgrounds and they are bigger than you, they are essentially as hard to deal with as someone a few belts above where their actual rank is at. Now add in the fact that Brock is a 300 lb former ncaa champion and he is punching you in the face.....good luck.
Brock dominated the ground game against Frank mir and Randy couture. Hunt has improved a lot there, but he was never going to have much luck against Brock on the ground.