I've never thought about it that way before, the problem of patriarchy as something ahistorical, or at least whose history is unaccounted for. Certainly feminism, from de Beauvoir to Butler and contemporary tumblr feminism, understands gender by and large as a social construct, so we certainly wouldn't take up an argument from biology, as you state, to resolve patriarchy in Marxist terms.

Gender, like class, (although class is the least visible and least talked about in the context of identity politics), is a contingent category. This seems in contrast to the humanist impulse of Marxism, for some reason, but I haven't read enough Marxist theory to cite. Capitalism, which has an ambivalent relation to gender and other axes of oppression, has been responsible for much of female and feminist liberation. An economic system that sees its subjects as first and foremost consumers allows their social integration regardless of categories of identity insofar as it profits from that integration. Women's sufferage and part in the war effort, their predominance as audience of advertising, particularly from the 1950s to the 1980s; capitalism was integral in if not altogether responsible for these social changes. And of course, capitalism is also intersectionally oppressive across gender lines. Feminism must recognize the way in which capitalism has benefitted women's social progress, and the relation we must work through as female socialists is not uncomplicated.

So, to your question, is it an a priori problem for Marxist feminism that patriarchy doesn't begin with capitalism? I would say nor. Otherness, after all, the logic on which gender and other binaries are constructed, has its roots in language itself. Even if capitalism does plenty to construct these categories by means of its ideological superstructure, class is the one which is most essential to capitalism's reproduction, most founded by it. Our rejection of feminism would itself be from a contradictory and ahistorical impulse if it were on the basis of the fact that patriarchy predates it. I expect that pure Marxism would do away with categories not only of class, but of race, of gender, of sexuality, at least insofar as these categories are constructed by it. What function does racial division, or racism, have, after all, in a classless society? Same for gender, misogyny and misandry. It does not follow that politics of race, like gender, like the social constructs that identitarian politics mean to subvert, "require a distortion of historical materialist methodology'" and we should only indulge them to not seem like dicks. Ideologies that construct these categories as essential are themselves essential to capitalism's reproduction; deconstruct those, and the revolution ought to follow.