If you're not concerned with it being sexist, why the focus on men and women? Would you be equally concerned if men and women were paid in aggregate the same, but the subclass of each that negotiated worse was paid less?

I just find it dishonest to frame the question as about men and women, as you did just now, if your concern is that people who negotiate a worse first salary are paid less. You're at best co-opting an unrelated issue.

I would say that in answer to your question, it's not fair, just as it wasn't when it happened to two men, but I'm not sure it's something we should change.

I'm also going to say that you should stop framing it as a gender equality issue when it's not -- it's a capitalism implementation issue.