Why Anne is the "Zeppo" of the Bronte sisters

Started reading Agnes Grey, the "Zeppo" of the Bronte sisters, the least-known Anne, and, well, it's surprisingly good after all, but from the first 100 pp or so (of about 400) you can see that she has neither the breadth and personal touch of sister Charlotte - the eponymous Agnes is not as distinct a character as Jane Eyre by any stretch, nor does she have the sense of drama, the imagination, the weirdness of Emily. In some ways, though, she combines the traits of the sisters with some of her own observations: the family - father a minor church figure, mother a diligent housewife, competent older sister, and Agnes the youngest - recalls the Bronte family is some ways: the family lives in almost complete isolation from the world at large. The father is impoverished (lost all his money in a foolish, risky investment), the mother and older daughter are so competent at all their tasks that they'd rather do everything themselves than have Agnes do anything - so she's a young woman without a place in the world who yearns for something greater, for a sense of worth (we can imagine a sisterly rivalry here). You'd literally think Agnes was 10 years old by the way she's treated but in fact she's 20 and goes off with family approval to work as a governess. Here's where the novel becomes odd and unsettling in the Bronte manner: the family she works for treats her horribly, and the children in her charge are complete monsters, especially the young boy who, aside from bossing around his younger siblings and throwing temper tantrums and fits and just about anything to bedevil Anne, gets great pleasure out of torturing animals - surely a sign then or now of serious mental illness. Eventually, Anne leaves this horrendous family and returns home. It makes, so far, for good reading, but there's a lack of nuance and complexity - the family is horrible, Agnes is good, etc. - that keeps the novel from rising to the first rank.