That's the crux of the matter. Most people unhappy about the 'pay gap' are indeed implying that employers are paying double (or 21% more) wage for a y chromoso

That's the crux of the matter. Most people unhappy about the 'pay gap' are indeed implying that employers are paying double (or 21% more) wage for a y chromosome. If the wage gap rather has to do with decisions employees make themselves (such as who stays home with the kids and thus works fewer hours / has less experience / doesn't get promoted) - then it's not really the problem of employers to contend with.