Women’s tennis is going through a bit of an odd period, as sports sometimes do. Only three women in the top ten have won grand-slam titles and even the most seasoned tennis observer would struggle to name, say, the winners of the past five grand-slam singles titles, something that most of us could manage without scratching our heads on the men’s side of the game.

But with Wimbledon upon us, we are all but guaranteed a couple of marquee names in the latter stages of the competition. Serena and Venus Williams have won seven of the past nine titles at SW19 and faced each other in three finals. Some would argue, paradoxically, that this sisterly monopolisation should be added to the charge sheet against women’s tennis, but it is here that I would part company with the critics.

If you ask me, the Williams sisters are good news not only for Wimbledon but for sport. It is not only that their improbable journey from the Watts suburb of Los Angeles to global stardom continues to inspire; it is not only that they have iconic status in a sport combating concerns about a lack of star quality; it is not only that they have smiles to light up a small city. It is also that they continue to thwack the ball with awesome power, to set about their opponents with thrust and gusto, to imbue women’s tennis with rare excitement.

Some will point out that the sisters are only part-timers, both involved with outside interests and parallel careers. They will say that it is difficult for fans to be properly committed to the sport when two of the leading lights are so agnostic.

But is it really, when you think about it, so very scandalous that two leading sports stars happen to have rounded world views? That sport is not an obsession but an outlet? That tennis is merely one aspect of their lives? Denis Healey, the former Chancellor of the Exchequer, called his interests outside politics a “hinterland” (in his case literature and photography), somewhere he could escape from the pressures and the anxieties and recharge the batteries. For Venus the hinterland is to be found in the world of fashion and interior design, where she has businesses and was involved in the design of the athletes’ apartments for the New York 2012 Olympic bid. Serena’s hinterland is found in her various activities in acting and entertainment.

I have no idea whether either of them are world class at what they get up to beyond the tennis court, but is that the point? One of the most difficult things for a sportsman or woman is coping with the strange, surreal and scary transition from the pinnacle (or near the pinnacle) of one profession to the bottom rung of the next after retirement. And what is certain is that the Williams sisters are way ahead of the game.

Perhaps the most intriguing thing of all about Venus and Serena is the nature and extent of their on-court rivalry. They have played each other on 20 occasions and are locked together at 10-10.

It is a strange and emotionally complex thing to face a sibling in a competitive arena. When I was coming through in table tennis my older brother, Andrew, was the leading junior in the country and we often clashed at competitions. Playing against him was never anything but traumatic. He was my practice partner, confidant and friend. We shared a house, a car to and from tournaments, and half our genes. Defeating him was the second most ghastly thing in the world. The only thing more ghastly? Losing to him.

Sibling rivalry represents a great Darwinian paradox: having to vanquish someone with whom you are so genetically interconnected, it almost feels like you have vanquished yourself. Is it any wonder that the Williams sisters look, at times, a little uncomfortable when facing each other down? That their battles lack just a bit of the bite and edge? That perhaps the biggest battle is the one within their souls?

But even if their contests are imbued with a complex dynamic, they are invariably watchable. The 2001 US Open final between the sisters was brought to primetime by US television, such was the upsurge in interest. On the wider point, note that CBS’s four highest-rated US Open women’s finals of the past decade involved Serena or Venus, or both.

It all leads to one conclusion: the Williams sisters remain the biggest draw and the greatest asset to women’s tennis.