Is structural discrimination a core belief of feminism?
It is not a core belief of feminism that women are through all times and societies worse off than men. It is core to feminism that sex and gender matter, and that they often shape power relations in a society. There are pluses and minuses to being dominant and to being subordinate. And indeed, feminists challenge the idea of predefined roles on the grounds that they limit freedom of choice, not only for women but for men also.
It is probably a core belief of most feminists that discrimination CAN be structural, that is, it can be produced by the institutions of society rather than any particular individual. This is a belief about the operation of social power and is shared by many social theorists, not specific to feminism.