To be fair about women only existing only in relation to Batman, that looks to me like every character, male and female, in this story. Dick, Alfred, Gordon, Supes, Hal don't fare any differently. We're seeing them all through Batman's eyes anyway, more than anybody else's.
I don't know if we can tell what Miller thinks about how women act or think from this title. an assertive woman is also necessarily a ballbuster. Again, I don't think we can tell from this title. Everybody's extreme here. Bizarre, even. Everything's amped up to 11 plus plus. WW, if that's who you're specifically referring to (I'm thinking you don't think BC falls into that category) she does have the one issue where she's absolutely bizarre and manhating crazy, then suddenly she and Superman are making out. So she doesn't end up assertive or nonassertive, imo. Just wouldn't know her if she didn't have the tiara on, ooc WW.
Black Canary is bizarre here too, but I would never say she's unassertive. She's bizarre, and often unheroic, but so is Batman.
Vicki Vale is frighteningly excited about her date and only dressed for extreme fanservice, but she takes care of business with the crooked cops and holds her own. Again, strange, fanservicey, is an idiot, but stands up to the cops and does her job.
Selina is treated more like an equal here (so far) than I've seen her treated in any of his previous work.