You're afraid to be corny, but I was born on the cob

I think it's interesting that the Beasts are conform to traditional gender roles, especially when compared to the Ancient Heroes. The warriors are men, and the women are in more nurturing positions. While Shadow Milk is far from traditionally masculine now, while he was still a Virtue, he was an academic – a position often seen as strictly for men. (And I feel it goes without saying that he almost certainly wasn't a shapeshifter until after his fall, given that his shifting is an extension of and aid for Shadow Milk's Deceit. That means no fluidity between masculine and feminine forms.)

Compare this to the Ancient Heroes. Pure Vanilla is an effeminate male healer (often voiced by women in different languages), and there are two strong warrior women. Dark Cacao and White Lily are the closest to being gender-conforming, but they still fall short, so to say. Dark Cacao is a strong king with a noted soft side, and White Lily is a delicate woman with a thirst for knowledge. (Remember: academia and knowledge are traditionally seen as men's territory.)

Furthermore, the Beasts have a majority of men, and the Ancient have a majority of women.

I like to imagine this is has to do with the fact that the Beasts were made for their roles, while the Ancient Heroes grew up as normal people before being gifted their sacred status. When the Virtues were hand-crafted, they were imagined up as 'suited' for their designated roles in every way. But, once these attempted manifestations of perfect ideals failed, it fell to normal people. And normal people are much more variant, much more diverse. But one can argue that it is also through the Ancient Heroes' upbringing as normal people that they are able to thrive where the Virtues once fell.