Given that reality, it is understandable to frame the "natural / primary" responsibilities assigned to or assumed by men and women in that light. The interesting thing about the Proclamation to the World, in my opinion, is that it appears to lay out this "natural" distinction and then say, in effect,
"Regardless of these natural responsibilities we inherit due strictly to biology and culture, the ideal marriage is one where such distinctions are erased - where each partner shares the other's responsibilities to some degree and acts as an equal partner with the other overall."
I understand completely how hard it is to accept that reading based on all the previous statements by leaders over the years, and the fact that "presiding over" still is used in various quotes, but the actual wording of the Proclamation says just that. Further, it says that each couple is obligated to make whatever adaptations are necessary for their marriage to work as well as possible. In essence, it says that the "ideal" is whatever works best for the individual couple - understanding that the "primary roles" are to provide and nurture. In other words, as long as a couple are united in providing for and nourishing their children, they are fulfilling their responsibilities as parents.
I view this as similar to the statement, "All men are created equal." First, it is the best they could do in their time (not including women in it); second, it articulated an ideal the society itself wasn't living (slavery) and couldn't live (and still doesn't live). Just as it was important to have the ideal written into a foundational government document, I think it's important to try to live and accept the ideal of the Proclamation with regard to raising one's children, even though our society (inside and outside the Church) isn't living and can't live it yet - and even though I believe the document itself is not perfect.