At this point, though, you would have conceded the point that women are not simply paid less than men on the basis of their sex, the earnings are actually a function of hours worked and seniority. The earnings gap would simply be a downstream effect of the new proposition you are putting forward, which is that the hours worked and seniority are denied to women on the basis of their sex.

This is not something that has been demonstrated to have been true, of course, but that would be the correct way of framing the argument.

No, it isn't, because controlling for those things means comparing the same job to the same job. The gap complaint is women being paid less for the exact same job and hours. It's different from the sexist glass ceiling.