I understand what you are saying about the difference in reading and understanding the Bible, and reading an admitted fictional novel. I am sure the term midrash as applied to this story could be seriously debated. But the authors intent to write about a family during a period of time where PM was the norm is clear in her focus on the interaction of the women in the story. The fact that we know these women already made the book that much more interesting to me.
This is some of the commentary I found when I went back to take a brief re-look at the novel to refresh my memory of it.
http://www.sparknotes.com/lit/redtent/context.html
(the author) "Diamant says “I did not set out to explain or rewrite the biblical text, but to use (the only daughter) Dinah’s silence to try to imagine what life was like for women in this historical period.”"
"In fact, those who are familiar with the story are often surprised by Diamant’s version: the author changes substantial portions of the Bible’s narrative, which focuses primarily on men and their relationships with God, in order to make her
novel a story of women and their relationships with one another."
"Modern midrashim attempt to make stories from the Bible more applicable to readers today. The term midrash is based on the Jewish word for “interpretation” or “exegesis.” Biblical stories about women tend to be abbreviated and seemingly less important, and many contemporary female writers have turned to the art of midrash-making to cast new light on such figures…."
Although in turn, I personally found that Jacob looked the same to me in both the Bible and in the novel. I believe that Gods plan was partially unfolded in Jacob's life thru the women he shared it with. And that God chose each woman for her individual example to those that followed to teach us more about that Plan.
Just my perspective. I honestly believe that all families work best with strong male leadership, and even better with strong female support.
Pat