Not.
Someone said in another thread that posters often just look at the opponent in a slam final to determine the toughness of competition. Nole fans will say that he faced 7-time Wimbledon champion Federer in the 2014 final, while Federer faced 0-time Wimbledon champion Roddick in the 2004 final, so Nole had the tougher competition. Wrong. 2014 Federer pales in comparison to the one who won 5 consecutive titles. And, it's not a given that Nole would win 2014 Wimbledon had he faced peak Roddick.
These posters also forget that it takes winning 6 matches to make a slam final. They love mentioning that Federer faced Gonzalez in the 2007 AO final, while not mentioning that he beat Youzhny, Djokovic, Robredo, and Roddick to reach the final.
That said, 2004 - 2007 Federer also faced peak Safin and young-gun Baghdatis in AO finals, faced peak Nadal in RG finals, faced peak Roddick/Nadal in Wimbledon finals (beat both players in 2007), and faced Agassi, Hewitt, Roddick, and Djokovic in the USO finals. Outside of finals, he faced the likes of Kuerten, Moya, Ferrero, Gaudio, Coria, and Nalbandian on clay, Hewitt, Henman, Ancic on grass, and many strong HC players, including Nalbandian, Davydenko, Haas, Blake, Karlovic, Stepanek, Ljubicic, and strong/improving young guns who would eventually become slam champions/finalists over the next several years.
As to the rest of your post, I disagree. Again, we're talking Djokovic, who many now call both the GOAT and HC GOAT. Not only should a peak Djokovic not lose to Nishikori, but he shouldn't lose to Murray or Wawrinka (who he had beaten 14 consecutive times heading into 2014). One could also argue that peak Nole shouldn't lose to Nadal at the USO (he definitely shouldn't lose without taking it to 5 sets!).