A saddle-mount can support a much heavier weapon than what the taur could hold and effectively use with their arms. Additionally, having two pairs of eyes and ears allows much greater situational awareness, and splitting the tasks of navigation and maneuvering from target acquisition and gunnery allows each set to be performed better, with specialised training.
The situational awareness and maneuver parts make sense, but consider too that carnivorae have a different spinal structure from equines. My fursona specifically needs a special saddle to distribute the weight properly just to safely handle any rider, and I wouldn't want to risk even a 50 lb gun in addition to the weight of a rider (not to mention, what would the recoil from that be like?)