You're missing the point in this discussion. It's not relevant at all how many sets women are playing; like any other job in this world you are being paid for your "marginal productivity"....in few words you are being paid for how much the others benefit from your work. A tennis player earns a lot of money because they're bringing money to the television, clients to the BNP Paribas, Nike, Adidas and so on. Why ? because they're popular and popularity bring money. Is that simple
If I'm not wrong, ATP is more popular than WTA so yeah, it's fair that the men should be paid more.
Why ATP is more popular....in part because of the tennis quality, it's true but as you all know already, not necessarily means that the most popular music or movies have also the highest quality...just put the girls playing shirtless on the court and you'll see how the audience will grow up.
The people who think that is unfair for female players to be paid less, ask yourself then if it's fair that the prize for winning a GS in tennis is1.000.000 $ and more and for winning the world judo championships they give you a nice big 5000$ check