Because we have these useful little things called speed figures that can help us use our minds as well as our eyes to evaluate horses.
Aside from that, he ran on a conveyor belt in the Juvy and got as good of a trip as a horse can get in the Derby. I'd say that should factor into the discussion that you think shouldn't happen because you linked to YouTube.
He was a good horse who also got extremely lucky in his Churchill wins. This idea that he was an indisputable horse for course is bizarre. He only won the Travers and was a head behind the horse of the year on other tracks.