I never thought that Whitaker was strong enough offensively to be considered an all-time great fighter. Much of his defense involved being to far away to hit back or not being in position to counter. Duran beats him, Emile Griffith beats him, Napoles, Luis Rodriguez, possibly Benitez. Buddy McGirt nearly won their first fight, fighting one-handed. Smart guys beat him.
Also, if he had tried a lot of his tricks (squatting to knee level, grabbing the opponent's leg in clinches, etc...) Duran (or Basilio or Zivic or Greb or Walker) would've kicked him in the face.