The “parity/depth versus mediocrity” debate is common for many sports, but it is used with particular frequency and vigor when evaluating the state of men’s and women’s tennis.

It could be one of the best arguments in sports because the debates are endless: Whatever we want to believe, we can believe forever because there’s no way to be specifically proven wrong. If a sport is dominated by a select few participants, it can be a sign of true greatness or terrible depth, depending on which way you choose to lean.

Take the 2010 Australian Open, for example. The first Slam of the 2010s could have been mistaken for any Slam of the past decade. On the men’s side, the top three seeds were Roger Federer, Rafael Nadal and Novak Djokovic; Nadal was the defending champion but fell to Andy Murray, who lost to Federer in the final. On the women’s side, top-seeded Serena Williams beat Petra Kvitova, Victoria Azarenka and Li Na en route to her fifth title in eight years.

The 2019 US Open, the decade’s final Slam, begins Monday in New York. Djokovic, Nadal and Federer are the top seeds in the men’s draw, while Naomi Osaka is the top women’s seed, with Williams the betting favorite to win her record-tying 24th career Grand Slam singles title. Same names on the men’s side; familiar icon on the women’s side, along with new names breaking through.

Wherever your statistical beliefs lie, though, the men’s and women’s tours have skewed down divergent paths of late despite the similar names at the top. A decade is an arbitrary amount of time when talking about trends or power shifts, but the end of a decade is still an interesting opportunity to step back and take stock.

Men’s game: The Big Three … and who else?

Over the past century, there had never been a decade with fewer than 11 different men’s Grand Slam champions. Despite Pete Sampras winning 12 Slams in the 1990s, 15 other men managed to win at least one. Despite Federer winning 15 in the 2000s, that decade still included 14 other title winners, from journeymen Thomas Johansson, Albert Costa and Gastón Gaudio to — gasp! — three different Americans.

This decade, however, there have been six total champions: Djokovic (15 titles), Nadal (12), Federer (five), Murray (three), Stan Wawrinka (three) and Marin Cilic (one). A look at previous decades on the men’s tour:

Champions versus multiple-time champions:

  • 1920s: 11 versus 7

  • 1930s: 18 versus 7

  • 1940s: 15 versus 5

  • 1950s: 17 versus 11

  • 1960s: 13 versus 6

  • 1970s: 16 versus 9

  • 1980s: 12 versus 8

  • 1990s: 16 versus 8

  • 2000s: 15 versus 7

  • 2010s: 6 versus 5

Things can get weird when your sport’s three best players of all time are taking the court in the same era.

The Big Three — Djokovic, Nadal and Federer — have combined for 32 Slams this decade and 54 overall. There is no historical comparison for that level of dominance. Federer, Nadal and Andre Agassi combined for 24 titles in the 2000s and 46 overall, but Agassi’s career was on its last legs when the decade began, and that’s still an inferior total. The only reasonably close decade is the 1960s, when Roy Emerson, Rod Laver and Manuel Santana combined for 27 titles. But those wins didn’t spill over into other decades, and the ’60s featured 13 different champs.

A handful of players have been capable of beating one of the Big Three (or Big Four, when Murray was healthy and in top form), but only two (Wawrinka and Cilic) have lifted a Grand Slam trophy.

Is that simply because of the Big Three/Four’s dominance? Or have Djokovic, Nadal, Federer and sometimes Murray been allowed to dominate for longer than they should because the generation of players behind them — Cilic, Kei Nishikori, Milos Raonic, Juan Martin del Potro, etc. — failed to step up?

Injuries have certainly played a role within this generation. Since winning the US Open 10 years ago, del Potro has missed 16 of 39 Slams with various lengthy rehabilitation stints (he is also out of this year’s Open because of recent knee surgery); Raonic has missed three of the past eight, and Nishikori has been at less than full strength for most of the past two years.

Nadal and Djokovic missed five Slams between them in the 2010s because of injuries, Federer missed one because of injury and skipped three French Opens, and Murray has played in only two of the past eight Slams. Those circumstances obviously didn’t hinder their development or stop them from dominating the tour.

The old bosses remain the bosses. This past year, Djokovic beat Nadal (Australian Open final) and Federer (Wimbledon final), while Nadal won his record 12th French Open title in between. One of the three has won the past 11 Slams.

A new generation of up-and-comers is providing intrigue, upside and entertainment. There are currently eight players age 23 or younger in the ATP top 30 rankings. Daniil Medvedev, 23, is up to fifth, while Felix Auger-Aliassime cracked the top 20 by his 19th birthday. Players like Dominic Thiem and Nick Kyrgios are just 25 and 24, but Thiem is the only player under 28 so far to reach a Slam final. He has lost twice against Nadal on the final Sunday at Roland Garros, dropping six of seven sets, and has yet to advance past the quarterfinals at any other Slam.

The Big Three and tennis fans continue to wait for a true, sustained challenge, and the US Open draw offers an interesting opportunity: Thiem, Stefanos Tsitsipas, Auger-Aliassime, Kyrgios, 20-year-old Denis Shapovalov and 21-year-old recent Federer-conqueror Andrey Rublev are all in the same quarter, tucked away from the Big Three. One could at least reach the semifinals.

Women’s game: An opposite phenomenon

Despite the fact that the best-of-three-sets format encourages more upsets than best-of-five (more variance is possible when you have to win fewer sets), women’s results at Slams have generally produced fewer champions per decade on average: 11 Slam champions and 5.8 multiple-Slam winners per decade since the 1970s, as opposed to 14.8 and eight, respectively, for the men.

Champions versus multiple-time champions:

  • 1920s: 9 versus 6

  • 1930s: 16 versus 10

  • 1940s: 9 versus 5

  • 1950s: 15 versus 9

  • 1960s: 11 versus 7

  • 1970s: 13 versus 6

  • 1980s: 7 versus 4

  • 1990s: 12 versus 5

  • 2000s: 12 versus 8

  • 2010s: 18 versus 10

You could ascribe that to a combination of poor depth and a more even distribution of the sport’s most dominant players: Chris Evert and Martina Navratilova passed the torch to Steffi Graf, who retired pretty soon after Serena and Venus Williams both began to build momentum. For the men, it appears Federer peaked a decade before Nadal, who peaked a decade before Djokovic.

This decade has been absolutely fascinating, though. Serena has won even more Slams in the 2010s (12) than in the 2000s (10). Despite that, nine other women won at least two Slams, and eight more won one:

Women’s Slam champions (2010s):

  • 12: Williams

  • 3: Angelique Kerber

  • 2: Victoria Azarenka, Kim Clijsters, Simona Halep, Petra Kvitova, Garbine Muguruza, Li Na, Naomi Osaka, Maria Sharapova

  • 1: Marion Bartoli, Ashleigh Barty, Jelena Ostapenko, Flavia Pennetta, Francesca Schiavone, Sloane Stephens, Samantha Stosur, Caroline Wozniacki

Those combined 18 champions marks the most the WTA has seen in a single decade — there previously had not been more than 13 in a decade in the modern era.

You can see whatever you want in the “depth versus mediocrity” argument. The “depth” argument gets a boost when you consider that, while Williams was clearly dominant, many women showed the capability of not only beating her, but dominating her in a tournament — think of Stosur in the 2011 US Open final (6-2, 6-3), Osaka in last year’s Open final (6-2, 6-4) or Halep this summer in the Wimbledon final (6-2, 6-2).

However, the clear lack of a No. 2 rival the past decade has been noticeable. Even if Kerber wins the US Open, this will be the first decade in the past 100 years in which we won’t have at least two players with five Slam victories. Williams has almost always had a chief rival of sorts, be it Sharapova, Azarenka, Kerber, etc., but the name has changed every year or two. And while there is plenty of upside on the list of 18 champs, there are also career journeywomen (Bartoli, Pennetta, Schiavone, Stosur) and young players who delivered enormous upside only to then wander into the wilderness (Ostapenko and, for at least part of 2019, Osaka).

Is that a sign of true depth? Before her Wimbledon run, Halep had fallen from No. 1 in the world at the start the season to No. 8 in mid-June; it could be considered a funk or a sign of inconsistency, but is it a funk if all 10 of her tour losses over that span came against players in the top 25? Or is it a sign the separation between a player of Halep’s caliber and the No. 20 player is smaller than it has ever been?

While you would love to see more consistency from certain high-upside players such as Osaka or Stephens, it seems the depth on the women’s tour has improved dramatically.