Novak Djokovic is a great, even brilliant, tennis player, but he is not the greatest of all time (GOAT). However, his diehard fans have tried to push the idea that he is the GOAT in recent years. While there is a potential argument here, primarily using the "weak era" argument whereby Roger Federer was playing against a lower calibre of opponent in his grand slam finals, their arguments ultimately fall flat for three reasons:
1. Djokovic has, so far, never won the Roland Garros crown, as those in contention for the GOAT label have. Until this happens, he is not a candidate, and this is something that so many Djokovic fans ignore. The players in contention are Rod Laver, Roger Federer and Rafael Nadal. Despite Pete Sampras' dominance of his generation, his inability to win on the clay of Roland Garros was primarily what prevented him from being able to eclipse Rod Laver as the GOAT at the time. Having won all 4 grand slams is a prerequisite for being in the running for the title of GOAT. However, this is especially relevant as Djokovic is now on the eve of what could be his insertion into the equation on his fourth consecutive attempt. That said, even if he does, there is arguably still headway that he needs to make in order to outdo the feats of those who have gone before him
2. People so quickly forget the level of tennis that many of Federer's opponents were playing at in their runs to the finals. Notably, Marcos Baghdatis (one who many cite as one of his lower level opponents), who made a run to the 2006 Australian Open final, came through many good opponents to be there. He was playing at a level far beyond what his ranking would suggest, as many commentators stated, really rendering the "average ranking of grand slam finals opponents" argument used to "show" Djokovic had more difficult opponents in his wins essentially moot. This is heavily tied to the next point
3. Racquet (string) technology and ball weight, and their relation to the overall game
Go Youtube the 2005 US Open final between Federer and Agassi. You will very quickly realise how different the climate of the game was barely over 10 years ago to as it is now. The primary difference is the speed of the rallies. Many tennis coaches now teach the idea of higher net clearance and greater levels of topspin, where this was of lesser emphasis in the past. The core reason for this meta-shift has been the advent and widespread use of polyester strings allowing for increased spin generation. Higher net clearance makes players less likely to lose points on account of hitting the net. Since the ball now goes up more than it used to, it physically takes longer to reach the other side of the court. Additionally, the weight of the tennis ball has also increased during recent times. This further contributes to the slowing of tennis overall. This meta-shift is highlighted in the 2012 Australian Open 4th round match between Djokovic and Lleyton Hewitt - perhaps the best defensive players of their generations.
In terms of world rankings, player rankings are far less labile than they used to be. While that can be put down to players being more consistent now, there is definitely more to it than that. The mid 2000s, and prior, more greatly rewarded the pure offensive player. Looking back through the history books, until Djokovic, the dominant players of any given generation were always primarily offensive players. Djokovic is really the first player to become completely dominant off the back of a game that is based upon a solid defence.
I posit that the lability of player rankings prior to the current generation was to do with net clearance. It takes strong mental focus to keep hitting lower balls as hard as what the top players of the ATP require because players are working with far lower margins for error. Multiply this across a whole match and it becomes quite mentally taxing. Multiply this across a whole year... You see where I am going with this. It was more difficult to maintain that level of focus (and thus a high level of tennis) in the past, and that is why there were far more ups and downs for any individual player.
Higher net clearance reduces the level to which a player needs to worry and lessens the burden of focus on players to some degree. I am not saying that Djokovic does not possess great mental fortitude (he does), but the fact that it was of greater importance in the past, comparatively, meant that players were somewhat more susceptible to how they were feeling on any given day, and made it more difficult to maintain a high level across a the span of a year. Since higher net clearance was also less of an option in the past, many players had no alternative and thus were forced into playing the offensive game that went hand-in-hand with the game of lower net clearance. This can be observed in the women's game, where the same meta-shift has not properly made its way in a widespread fashion, and players are very much still plagued by the issues that the men's game faced over 10 years ago. Now, with the ability to wholly use higher net clearance, the better players in today's game are ones with strong defense, or at least the capability to do so. This has also, fortunately or unfortunately, somewhat homogenised tennis across all different surfaces.
Ultimately, players of the past who made showings late in grand slams were often the players who had displayed the greatest mental fortitude in being able to attack effectively and relentlessly over that span of two weeks, rather than the most consistent players that we see more of today with the likes of Djokovic and Andy Murray. What this means is that the idea of Djokovic having had stronger (read: higher ranked) opponents is less to do with the calibre of players he faced, but rather the unpredictability and fickle nature of who would display the greatest mental fortitude for the span of the two weeks of a grand slam. The consistent players of past generations were rarely able to gain any real traction, and this came down to technology not favouring them as it does now.
Now, what does this all have to do with Djokovic being unloved? Many anti-Djokovic fans will tend to bring up the ideas that he is "arrogant" and a "buffoon" etc. While those qualities are generally negative, he is arguably not significantly different to players of other generations in this regard. Yet, Djokovic does not receive the same praise and adoration as those who have gone before him.
One idea that is not often talked about in depth is the idea of being associated as a "fan of x player". It is a very subversive idea, but one that I believe is very pervasive, affecting nearly all those who have considered being associated as a Djokovic fan and subsequently chosen not to. For people who are unaware, being a Djokovic fan often comes with the connotation of being a belligerent individual who can't see reason despite the facts being put in front of them. This stems from the fact that many Djokovic fans continue to claim that he is the GOAT in spite of all the evidence and analysis to the contrary (i.e. all of the above), never provide any substantiated evidence of their own, and take the stance of "nananana who's number 1 now I'm not listening to you" when presented with actual evidence.
This stereotype is an unfortunate one as it brings a polarising negativity towards Djokovic, and one that is heavily unwarranted. Why his diehard fans are the way they are is up for debate, but one thing remains about them - they respond with nothing but belligerence when talking about their man. This is perhaps the biggest reason that Djokovic will likely never win the same level of love and praise that his contemporaries, Federer and Nadal, have.