The parent comment to yours was poorly worded and snarky, so you have a right to be upset. But still, I think your reasoning is flawed. People are generally promoted by their competence and their negotiating/office politics skills, and you can't claim that those are the same across all genders. Why would women, who are fundamentally different than men, have the exact same competence and negotiating abilities as men? There's no reason the two genders should be equal.
If you really have two equally skilled engineers, one male, one female, and only the male is promoted, that's sexism. But two engineers are never the same, so you can't make that argument.
But say I'm doing a project in Java and they are about equal, I keep giving Al the meaty work then use it justify a promotion, which I can't justify for Marcy. It's not that she's that much worse, I just never gave her the chance to prove it (blah blah peter principle, perform at next level, etc...). That just might be a bit sexist.
Have you really never worked on a project where the golden boy was the face of everything and everyone else was ignored?