Why what is wrong? That there is a pay disparity? That doesnt mean a damn thing to be honest. There could be a lot of reasons why there is a pay disparity.
What you are doing is the same thing as people were doing with the wage gap. The only thing is people werent looking at peoples wages but instead of yearly earnings, took the 2 numbers and ran with it. Just saying Sally makes 10 dollars and David makes 15 doesnt mean anything at all. Sally could be worse at her job, doesnt work as much, didnt negotiate her salary, doesnt meet deadlines. There are many reasons why David could make more. Its the people sueing that has to prove that they are being discriminated against and a disparity isnt enough to make any final judgement.