This kind of reasoning is stupid beyond any limits. It's kind of like observing bacteria and claim that it multiplies indefinitely and expands indefinitely. Well, there are some other constraints beyond mere pussy and not all women are able to bear children nor or in the future. I still don't see at least women over 45 being drafted and neither do I see a fertility check before giving women a pu$$y pass. Even most of these fertile women in Ukraine will likely not bear more than 1 or 2 kids in their lifetime, if any.

There are two main constraints that trump mere count of fertile women: expectation of resources in order to start a family and ability to produce those resources. Historically, housing space was the main factor. If you look through war campaigns and their aftermath, high fertility of 4+ children meant the population would quickly reach its theoretical peak, given their production constraints. But destruction of crops meant short-term collapse that was usually worse than sheer number of deaths, while destruction of homes meant longer-term demographic collapse, due to high complexity, time and effort necessary to build housing space all the way until modern age. Main factor affecting population plunge in 30-year war was related to Swedish campaigns of scorched earth, destroying thousands of villages and cities. Places affected by plague would simply be repopulated by new inhabitants, or by newborns if homes weren't left completely empty. Swedish intervention, however, had a long-lasting effect due to destruction of housing space.

Why is this story about resources important? Well, connect the dots. It's men who produce more than women in general. Having an excess of men effectively means having more births in the long run, as long as they can produce the expected amount of resources. This becomes apparent in utilization of "partial genocides" and ethnic cleansing in zones or areas where militaries or political leaders opine that they don't have time, resources or political (external) support to outright focus and kill everyone in opposing ethnic, religious or other group. In just about every historical campaign of such sort, they resort to kill off men of productive age or near productive age and it's not just due to military strength. Reason why they avoid killing i.e. 4 y/o boys is because same women would likely tend to give birth to desires number of children, thus they'll likely tend to give new births. 14 y/o boys? Well, enough resources were invested to make it valuable and they're likely near that cutoff so they're likely going to be targeted. Men over 70 y/o? Well they slowly become burden to general society so they're likely going to be left alive. Same approach is historically seen in mutilating primarily men of working age or close to it (by blinding them or cutting their arm or leg). And there's also a trend of killing off the elites among highly skilled individuals such as doctors, lawyers and highly specialized technicians, where the targets are often both men AND women. You can also connect the dots why women are targeted.

Anyways, each time such "partial genocide" was done, history attests a very calculated approach and pragmatism, with the aim or inflictimg even worse damage in the long run than it would be if they killed all people they laid their hands on. A good example would be blinding of Bulgarian army by the Byzanties, with leaving few men to guide them back to their homes. This approach turned Bulgarian Empire, a powerful adversary to Byzantine emperor at the time, into a failed state.

In essence, your hypothetical answer about 1:400 ratio is unrealistic and doesn't bode well with real-life scenarios and gender ratios. A ratio of 105 men and 95 women vs 95 men and 105 women will likely produce higher total fertility for the group with excess men, all other factors being equal. But before you jump to conclusions, don't forget that other factor we see way too often in our modern era: anticipated resources in order to start a family. It's very apparent that wealthier societies tend to have less children per woman than poorer societies - but only those that didn't go through transition of our modern era of thinking.

An African village likely still has 5+ kids vs Chinese cities that have less than 1 kid per woman. Gender ratio at birth in Africa is generally lower than anywhere else, while gender ratio in China is significantly skewed with the excess of men. However, a good comparison would be a similar village with similar mentality in Africa, with excess men vs village with lack of men. Fertility of women in a village with surplus of men will tend to increase because women tend to pair off with more successful men among those in control group, while fertility of single women or women who share a man also tend to decrease than controlled group, even if their man has more resources. A good example of women belonging to harem having less children than anticipated in their contemporary era? Well, just make a comparison to any polygynous society prior to 19th century. Even women of powerful and wealthy Muslim rulers exhibited this behavior. I.e. Moroccan ruler Ismail, dubbed the father with the most children, had over 500 wives and over 800 children. In terms of fertility of ordinary women of its era in Morocco and projected death of about 1/3 of children in their infancy, this meant that it's well below replacement level. This isn't an exception, but a general rule and while it's obvious that 500 men and 1 woman would result with way less children than that, case still stands: in a common post-war gender ratio, lack of men would tend to effectively decrease the fertility rate.