Biases aside, here's the thing that I've always thought completely distinguishes the physical/athletic demands of playing hockey. Every single skater must possess the full fleet of athletic traits (i.e., speed, strength coordination, stamina, flexibility, etc.) in order to compete at a high level. No one is specialized to a point where they are an exception. Okay, a person could argue that goalies are, and I would disagree, but whatever. In baseball, some people run, and some people don't. In basketball, some people are quick and hyper coordinated, and some are big and imposing, yet slower than average. In football, you probably have some of the freakiest freaks in all the world, and you also have a lot of hulking strongmen who can't get down field without an oxygen tank. Other sports, more examples. It goes on like this.