Lennert, you confuse old poly setting to modern poly setting. Yes, western women had more right in social, financial and educational aspects, yet, their sexiuality was still determined by the society. Women were still subjected to social expectations on procreation and how the express their sexuality.

But the modern poly setting does not restrict women as such. Which is why we are sesing marriage over 20 years crash.

https://www.everydayhealth.com/emotional-health/why-more-couples-are-divorcing-at-older-ages-than-before-and-what-you-can-do-to-avoid-it/

You know it do you some good to get acquainted with the changes in our social and sexual structure. As women become more confident in themselves (earning a living without depending on men) the more we lean towards polyamory. Because it gives us more power over our sexuality like you cleared stated.

In other words, if men are dating more women at the same time, women will do the same. Therefore, the problem of infidelity and jealousy associated with mono relationship will be at minimal.

If I remember correctly, a community in India already practices open relationship style. There everyone can have sex with just anybody. And yet, they live in harmony. I will try and get the name of the community and update this comment.
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Updated: The community I'm taking about is Muria tribe. The unmarried are nit restricted to one sexual partner. You can read up about them on Google.

https://www.nature.com/articles/164249a0

So it's possible adopting modern poly setting will be better for both men and women. Those who choose mono relationships will do as a choice not from pressure.