This horror story is a reflection of what a unisex prison would be like. Not real society. Although it has similarities for sure.
So the inbreeding caused a bunch of Incels, Chads and Pretty Boys, to pop up. OK the damning part is the women turning into men.
If the scientist had connected the universes using tunnels. The women would have been able to find less related rats, and therefore get rid of some of those hyper masculine genes.
All humans living in a single city, controlled by a 1 world government, is viable, as long as the city is big enough to were females can find men that don't have the same last name.