It's a very complex topic with a multitude of answers, frankly. I disagree with you boiling it down to a single facet of the whole affair.
I agree that there's more going on, but it's an undeniable fact that, culturally, there are higher standards for women than there are for men, with the examples I've given (make-up, clothing, hairstyles) being principally manifestations of that culture. So in the context of this "morals reversal" manga, that dynamic should be reversed, with there being higher standards for men than there are for women. I'm not mentioning other aspects of this overarching dynamic because I'm specifically commenting on this manga's world apparently having higher standards for women than our own in regards to chest size.
