The fastest horse ever recorded was a Quarter Horse going 55 mph. There is a reason that it is Thoroughbreds and not Quarter Horses that race in the Kentucky Derby -- which is 1.25 miles, and Arabians race in long distance races. The argument being made for horses here grabs the Quarter Horse with a 55 mph world record and applies that to everything. The trouble is, the Quarter Horse has the same problem as the cheetah. It has a quick burst of speed, but can't sustain that speed over distances. They're called the Quarter Horses because they race the quarter mile. The fastest horse on earth has about the same full on sprint range as the cheetah.
If you want your horse to run all day, then you want an Arabian. The fastest Arabian ever recorded is 40 mph, quite a bit slower than your Quarter Horse -- the sprinting specialist. With a bit less focused selective breeding and public interest, the fastest greyhound ever is 45 mph. Faster than the fastest Arabian but slower than the fastest Quarter Horse. So with similar amounts of human meddling over the centuries, the dog -- same species as the wolf -- ends up about as fast as the horse. And when you come right down to averages, the average wolf can outrun the average horse.
Horses are not the fastest creature in the world by a long shot. Not in short sprints. Not over distances. They were ridden for millennia because they are pretty fast, that can be well trained, and carry a human body on their back.