Wouldn't your causal mechanism be disproven by the reams of peaceful countries without such imbalances? In any case, the natural overproduction of males versus females at birth is too tiny to explain these gulfs.
As I understand it, the grandparent's argument is that earlier on in history, wars (and violence in general) would cause a reduction in the percentage of males. For example[0], in Soviet Russia following WW2, the ratio of young men/women dropped to 0.7. And that given that the China and India are more peaceful now (for various reasons), this violent force does not come into effect.
I don't understand how your response is relevant to the above argument.
Peaceful countries with balanced population has better woman rights. What China/India has, isn’t really natural because they tend to abort female babies.
I don't understand how your response is relevant to the above argument.
[0] https://www.ucis.pitt.edu/nceeer/2007_820-4g_Brainerd1.pdf