Write the story you have within you. If your significant characters are all female, that is fine. If everyone in your universe is female, that might seem a trifle odd unless it is called for by your paradigm.
The question to ask yourself is, does their gender serve the story? Does it violate a trope and create an intriguing spin on an otherwise tired tale? Is there a reason they are female?
The film Columbiana was intriguing in part because the assassin was female. She was an angel of vengeance who went pro but still accomplished her quest.
Regarding an even split between genders in existing works, I find that more true of Jane Austen’s works than more recent ones. Most novels are populated by men. I was reading my current work to a friend and in the third paragraph I used the feminine pronoun, announcing to my audience that the secondary protag is a woman. My friend said ‘Where’d the girl come from?’. I told him she was there all the time.
My secondary protag is tough and brave and one of my cousins loves her, thinks she is bad ass and wonderful.
My point is this; expectations in the reader’s mind are such that any deviation from the norm might set some back on their heels, but that same choice has another going ‘Hell yeah!’. The friend who was startled by her gender came to like her - not as much as my main, but that is okay.
Do not pander to an imagined audience. Write the story about your characters and if they are well developed and intriguing, you have something. If they are check boxes and cardboard cutouts, they need work.
Have a reason for the choices you make and have that reason be your own. Do not let others tell you that you need to include a character who is X, but include such if that character being X adds to your story.
Diversity is great, but we seek to tell the best story we can and if that is about a group of five women who pursue and accomplish their goals, fine. If it is about five people who, because of an outside agenda or a desire to fill a niche must be X, you might want to reconsider it. Readers are not stupid and they will see, if the latter, that it is skewing towards propaganda, but if the former you have no worries.
I would rather read a story about one fascinating character than a group of half drawn, flat ones.
What wetcircuit says about range in roles and characters within one gender is true. There are strong, brave, clever, devious, evil, virtuous and weak women - just avoid dumping all characteristics in one soul.
Give each something they excel at, and something they just don’t do well. Give them hopes and fears, strengths and weaknesses and the physical package they exist in will have less meaning. Give them a soul.