i'm a very very complex person

What makes a story believable or not, for me, is the element of friendship. Of course, there are other elements, like writing and style, that are so important but also so hard to define. But you mention that the friendships in the Atwood book are rarely explicated, though these women are supposed to be close and they share an experience that defines the book. It's easy to write about the chemistry of romance, in my opinion, but not so easy to write about friendship in a way that's meaningful and geniune and interesting.