Does Kesey really argue that women are less powerful than men? Why is it that Nurse Ratched loses her power when McMurphy reveals her breasts?

While it is true that her breasts are the most obvious symbol of her womanhood, the reality is that she is still in charge.  Even though for a moment she "loses" some power, she is ultimately the one who controls the men and their futures.  If we equate power to control, then Nurst Ratched is a very powerful woman.