Kind of a straw man? Upright bipedal forms are very efficient for running, especially in uneven or obstructed terrain. Horses are good for level plains; many other runners are bipedal.
I don't think domesticated prey/herd animals are good examples to compare capabilities.
IMHO, the human leg/knee/ankle/feet are not well designed. Mountain goats (Dall Sheep, for instance), pumas, and most larger working dogs and cats seem to fly in the face of your statement about handling obstructed terrain.
Quads rule.