After playing fast and loose with numbers and models (and assuming a metric ton on things), I can now say with no authority at all that the optimal level of female-friendly content for a book like Batman is about 0.25 (0.259259..., to be meaninglessly precise). This is equivalent to content that would make it as attractive to a putatively average female potential comic books reader as Outsiders or Legion is to the average (male) comic books reader.
Not too much, right? And yet that move would raise its sales -long term- about 70%, even taking into account an hypothetically reduced male readership. It'd sell more than ASB&R. It'd earn DC Comics an extra USD 175,000 a month. Handwaving a lot, and even taking into account record high rates in the US, the financial net present value for DC Comics of making this change is above 30 million dollars.
That's 30 million dollars free for the taking. All they need to do is stop putting women in refrigerators in the Batman title alone.