I would consider this poem to speak against patriarchy because Plath rebels not only against her father and everything he represents but also against her husband, and she associates the authority and villainy of both with men (and patriarchal power) in general. She has felt confined and trapped by her father, like a foot within a black shoe in which it cannot move. Her father, she says, was like a "bag full of God"—authoritative and looming large over a young woman's life—and she used to "pray to recover" him after he died because he was all she knew. Like the rule of patriarchy, his influence was everywhere. As she grew, she came to realize that men were responsible for the "wars, wars, wars," and she felt stuck, unable to speak her father's language. She felt herself becoming his enemy, someone on whom he would look down.
Everything Plath says of her father could also be said, often figuratively, about women's relationships to men in general, especially during the era in which she lived. She saw her father as a devil who broke her heart, and then she grew up and found a man just like her father, and married him. She compares this man, like her father, to a vampire, a villain. Her husband drained her of life, just as the patriarchy does to women; they become voiceless and feel powerless to rebel against misogynist notions of what women ought to be. Plath rebels against the male power in her life, showing that such a thing is possible.