When discussing something like how a particular text "represents" something as broad as "women," there are lots of different factors to take into account before deciding on your particular point of you. They can probably be broken down into a few key questions:
1) What function do the female characters serve in the story?
We often address this question in terms of a key word, "agency." Agency basically means the power to make choices, affect decisions and control your own path. If one character has "agency" and another does not, it means that one character controls the story, and other characters are subservient to that control. Iran, for example, does not have "agency," and really only exists for us to learn more about Deckard's character. It could be argued, however, that Rachel does have a degree of agency as she affects Deckard and the plot, though it is arguable how much control she has over the proceedings and whether she remains a character who serves the wider purposes of the male protagonist.
If female characters don't have agency, as is often the case, then the story becomes about male characters, and does not actually represent any concrete idea of femininity or female identity outside the confines of men. It might be said to "under-represent" the characters or, to be blunt, be a bit sexist.
2) What do the female characters represent about femininity?
Our gender is part of our identity as human beings, just as a character's gender is a part of their identity. How does the story represent that crucial aspect as affecting their characterization, and what does that encourage us to think about gender as whole? If a character seems strong and brave as part of his male identity (as could be argued with Deckard) then that might mean the text is suggesting that part of being a man is being brave. How is Rachel represented in the text? Is that because she is a woman?
3) Are characters defined by their "femininity"?
This process can go too far, though. An important part of characterization is complexity. Deckard is not JUST male, he is also defined by his job, his background, his education and lots of other qualities. Is his wife JUST a woman though? Does she transcend her characterization based on gender to feel like a real character? Pris, for example, is pretty much defined by her gender, acting as a stereotypical female at all times. This is also an issue when it comes to representation.
Think about all these issues and decide for yourself. The question isn't really one of "over" or "under" representation, but rather one of how they are represented and what that representation is.
Women certainly are underrepresented in Dick's Do Androids Dream of Electric Sheep?
In fact, there is only one (actual) woman in the novel and that is Deckard's wife Iran. All the others, Rachel Rosen, Luba Luft, Pris Stratton and Irmgard Baty are actually female androids. And its not only the under-representation but somewhat unfair representation as well. Deckard's wife misuses her artificial brain simulator and is physically and emotionally imperfect, while the female androids employ sexual favors to escape the bounty hunters. In fact, Rachel confesses having slept with multiple bounty-hunters to protect Rachel-model androids. She is also shown to be vengeful (she kills Deckard's goat). Similarly, Pris is depicted as manipulative and cruel. The male androids are not focused on, and the story revolves around female androids and Deckard's attempts to collect bounty while contemplating his confusion over nature vs. artifice.
All in all, the women are not only under-represented but unfairly represented as well.