This is a common misconception. The "separate spheres" theory of gender roles, which you aptly refer to as "separate but equal," is really a product of the 19th century. Prior to that time, the vast majority of people didn't have the economic resources for that kind of segregation. At planting and harvest time especially, everyone was in the field pretty much equally. Of course there was some division of labor by gender, but not anything like what was seen in the 19th century. Gender segregation, and rigidly defined gender roles, were luxuries for the rich. The 19th century was somewhat unique because there was enough material prosperity that a large proportion of families could afford this "luxury," but not enough prosperity to start freeing women from full time household drudgery.
On a side note, I don't have much love for third-wave feminists, but I think they do have a point that our perceptions of gender roles are very heavily skewed towards the upper and middle-class perspective, especially when looking back at historical accounts. I always found it strange in history class that when the American feminist movement was covered, the experience of women in the 40's and 50's didn't resemble the life that either of my grandmothers lived very much. The women in the history books were all upper/middle class, whereas one of my grandmothers was a riveter, and the other worked as a farm-hand before scraping together enough money to train to be a secretary. Both married in their late thirties after living on their own for 15-20 years. Not working, or being dependent on/subservient to a man, was not an option for them.