Huh, really? I thought there were slightly more women than men, but maybe that depends on the economies etc.
As for your second point, yes, exactly. They don't reproduce. So it doesn't matter if many men get one wife each, or if a few men get many wives each, the number of pregnancies won't change, and the number of pregnancy-related deaths won't change either. So (again), I don't see how polygyny helps in this situation.
Ich stelle mir einfach einen quadratischen Fernseher vor, der genauso groß ist wie eine Schultafel...