So I ask the simple question, how SHOULD women who are IN Christ and IMAGE BEARERS of God read the book of Esther? Well, first, the way I've worded the question sets me up as an authority that I am not. Second, it sounds like you are obligated to agree with my analysis, but that's not true either. As I often say, this blog is just a lecture to myself, so I'm really only answering the question how should this Christian woman (me) who values submission think of Vashti and Esther. Maybe I'll say something here that the Spirit causes to resonate with you, and that's good too.
There are a few principles that help me navigate the story of Esther. First, I must remember with any story in Scripture the very great difference in DESCRIPTIVE and PRESCRIPTIVE passages. Many, many times in the Bible, particularly the Old Testament, we are given stories without commentary that we are not ever intended to embrace as examples to us. Don't cut up your concubine and spread her remains around the camp of those who murdered her. And please don't kill your daughter as a sacrifice just because she's the first one to walk out a tent after you make a vow to God. It's not a good idea to lay down in the middle of the night at the foot of the bed of a man whose attention you are hoping to land. And we don't prescribe that all widows move in with their mother in law and marry their husband's cousin just because the book of Ruth describes that scenario.
Second, Scripture is the best commentary on itself. We know from Genesis 2 that woman was created to be a strong helper in the image of God. That certainly reflects on Esther—she was strong for the children of God, helping to protect them by potentially sacrificing her own life to get the ear of the king. We also know from Genesis 3 that the curse among other things is that man oppresses woman (see here and here). Well, boy howdy, that certainly reflects on the story of Vashti and Esther. There is no indication of any virtue in the king towards women in that story. God's people are basically in captivity and the king demonstrates no faith in God. He's not the worst of kings, evidenced by the fact he didn't kill Vashti. But he's obviously feared—Esther keeps the fact she is Jewish secret from him at the start. And he is willing to wipe out an entire people, male and female, based on Haman's flimsy reasoning of their threat to his kingship. The king has a harem and concubines. There is nothing about him that reflects virtue or goodness.
In terms of Ephesians 5 and wifely submission, Esther does submit, but not to the king. She submits to Mordecai, who is neither her husband or father—when he says don't tell the king you're Jewish, she doesn't. When Mordecai encouraged her to defy the king's orders by approaching him about sparing the Jews, she does. In the end, there is nothing about Esther's story that can be reasonably construed as having anything to do with wifely submission in terms of Ephesians 5.
Here is what Esther teaches us as Christian women who value submission.
1) Nothing about submission.
2) Everything about the sovereignty of God.
Esther is a beautiful book, much like Ruth, on God's supernatural moving behind the scenes to preserve His people, particularly the line of the Messiah. To this end, Vashti's refusal is as much a part of God's sovereign plan to move Esther into the place where she could advocate for God's people as Esther's promotion to queen.
If you want to understand what God prescribes about help, submission, headship, and respect, don't read Esther for advice or example. However, the book of Esther has much to teach us about our sovereign Father in heaven who wrote a story before time began and declared it FINISHED on the cross. When we face uncertainties in life, the same God who is never mentioned in Esther is the same one flying under the radar at times in our life. He holds it all together though, and His plan will be accomplished.
Colossians 1 16 For by him (Jesus) all things were created, in heaven and on earth, visible and invisible, whether thrones or dominions or rulers or authorities—all things were created through him and for him. 17 And he is before all things, and in him all things hold together.