His best performance was a loss? Strange.
Santana seemed to be a tougher fighter than Gimeno, giving Laver a tough one at Wimbledon in 1962, and, most memorably, winning the 1961 Roland Garros with close, comeback five-set wins over Laver, Emerson, and Pietrangeli in the last three rounds.
Gimeno seemed to fold when challenged, but could win on clay when it wasn't at RG.
His 1972 RG win came with only two realistic challenges, from Smith (who lost in three sets, clay not being his thing), and from Metreveli in five sets (a good, but not great player).
It is important to look at the strength of the field, and not simply list titles.
Not strange to me. I can think of occasions when a players' absolute best tennis still results in a loss, to an opponent who is either in a whole different league, or is playing in the 'zone'. Matter of fact I think it might be a good thread.