The name of the game is MONEY, and Gimeno never attained the status of Santana in the public mind because Gimeno jumped at pro contracts BEFORE he accomplished anything significant in the amateur ranks.
Emerson and Santana stayed amateur because of the economics of the game, because Laver and Rosewall, for all their skill in the mid-1960's, did not command the drawing power of Hoad and Gonzales in the late 1950's and the ability to rent out the major venues; Forest Hills, Roland Garros, Kooyong. Instead, it was Longwood (Boston, not the Big Apple), Stade Coubertin (cheaper, indoor, and no clay!), and Melbourne Arena. A sad decline for the pro game.
No wonder the pros could not offer Emerson and Santana enough contract to overcome the increased funds in the amateur game and a more aggressive cash offer to keep the top amateur stars.
I am not sure that Gimeno could outperform Santana on clay or grass in the mid-1960's. In 1970, Santana beat Laver and Hoad to win at Barcelona, against a field that included Gimeno, and teamed with Hoad to beat Laver and Gimeno in the doubles final.
Gimeno won the French Open while Santana did not. You cannot consider only one tournament. Gimeno was a top ten player in a few open era years, Santana not.