Just watching Gene dance is a joy. He's having fun and it's as easy as breathing for the rest of us. Other dancers to include Fosse, Cole, Champion, etc., could not put it all together and did not have the public persona that Gene possessed. So many dancers, great in their own right, moved into choreography and found success. Gene did that too, but was so valuable in front of the camera, most people don't know that he choreographed all of his dances and directed some of his movies, not to mention defining dance on film.
Watch this clip from An American in Paris and simply see the joy and ease of movement Gene displays. He floats. It's not work. He's not even breaking a sweat.