I don't blame them entirely for feeling that way, it's such a male-dominated industry.
But there's little reward to banding together, they're in the minority in the firm. I'm hoping things change, but...

Joan can't get over how far Peggy has come; I think she still sees herself as Peg's superior and it irks her that she can't just override her.

Peggy can't get over Joan's power and beauty; I think she envies Joan a lot for her looks; I'm pretty sure Peggy would use looks to her advantage, even if it wasn't the pic type of attention...she's pretty money oriented.