So those were the objections against PUA. Now the post itself...

A big part of the power a woman has over her mate is the threat of withdrawing from him sexually and/or emotionally....I still believe that women in general tend to have more power but PU shifted this towards men. W will have to consider "If I withdraw he can find another woman in two weeks.", she clearly has lost bargaining power. P knows it too and will weigh if it is worth the hassle to remain in the relationship if he can find another woman very quickly. P has more power for being a PUA than he would have if he weren't.

This is called an unhealthy relationship. Using the threat of leaving a relationship as a bargaining chip, to blackmail people, is emotional abuse. It's far better to be alone than to have a relationship like this, in my opinion.

But back to the premise. If it's all about supply and demand and power equilibrium, wouldn't men object to fashion and beauty products by the same logic? Wouldn't women object to men working out?

Good looking women will have no problem attracting lots of interested males. Usually women do the choosing, while males compete for the attention.

Warning: Anecdotal evidence - "Easier for women" only applies to casual sex. It is more or less equally hard for both genders to enter a long term relationship, and varies from social circle to circle as a function of gender ratio.