When we say reproductive value, we’re applying a supply demand metaphor from economics to each sex, then comparing their values in a hypothetical underlying currency. Supply and demand fluctuate but, as you said, we are born in about a 50/50 ratio, so absent major upsets to the ratio post-birth like wars, we should expect there to be roughly one man for each woman. Then demand (for men) is the thing that must be low to reduce their value. But it would be a bit silly to say women just aren’t interested in men in general, so I have to assume your complaint is that women in aggregate don’t have equal demand for all men. We’re not talking about the reproductive value of men in general, nor about a biological process removed from society, but a social phenomenon wherein demand for men by women is distributed unevenly among them. An undesirable man might be said to have a low reproductive value and a desirable man a high one. In aggregate, it wouldn’t make sense to say men have a low reproductive value.