Gordie Howe played for 26 seasons and scored over 70 points in 21 straight seasons. No one in hockey can match that stat. He won Stanley Cups and he won scoring titles. He even played with his sons, on the same team! And he was better then them!
Gretzky took the #99 because he said he would be twice as good as Howe (#9) He may not have been "twice as good" but he was undoubtably the best. I think you would be hard pressed to find anyone in professional sports that has so obviously dominated their sport at a level so far above their counterparts.
Jordan had to contend with Magic, Dominique, Isiah, Larry etc as contemporaries. The closets Gretzky had was Lemieux.