There may be some truth in that, but others would argue that the agricultural societies which predated the Industrial Revolution were just as "unnatural", and Jared Diamond even believes that the Agricultural Revolution was the worst mistake in human history.
In this New York Times article, John Tierney says that differences between men and women appear to be greater in wealthy societies that in traditional ones
It looks as if personality differences between men and women are smaller in traditional cultures like India’s or Zimbabwe’s than in the Netherlands or the United States. A husband and a stay-at-home wife in a patriarchal Botswanan clan seem to be more alike than a working couple in Denmark or France.and that this is because of changes in the personalities of men
The biggest changes recorded by the researchers involve the personalities of men, not women. Men in traditional agricultural societies and poorer countries seem more cautious and anxious, less assertive and less competitive than men in the most progressive and rich countries of Europe and North America.
To explain these differences, Dr. Schmitt and his collaborators from Austria and Estonia point to the hardships of life in poorer countries. They note that in some other species, environmental stress tends to disproportionately affect the larger sex and mute costly secondary sexual characteristics (like male birds’ displays of plumage). And, they say, there are examples of stress muting biological sex differences in humans. For instance, the average disparity in height between men and women isn’t as pronounced in poor countries as it is in rich countries, because boys’ growth is disproportionately stunted by stresses like malnutrition and disease.
This seems to imply that the stresses on health were due to the absolute poverty of the societies, rather than due to inequality. However, both the work of Jared Diamond, and the Whitehall studies emphasize that inequality itself can cause serious health problems for the teeming multitudes at the base of the pyramid (though I think Jared Diamond suggests that this is through a Malthusian mechanism and so would be resolved with increased per-capita availability of food). I wonder how inequality and increasing affluence jointly affect personality. We already have an idea as to the effect on physical well-being.
My guess is that if both median wealth and inequality increase, we can expect men to become more aggressive because their "down-side" is that much less (they are unlikely to starve to death) and the "up-side" is greater (they have more to gain by trying their hand). Some elementary option theory, maybe?