I think one of the reasons it fell apart was because Kira looked so out of place doing things that Dax wanted to do. I mean that scene in Way of the Warrior where they were in the holodeck and then first meet Worf, that was close to an embarrassing scene for Kira.
Yeah, that was awful. DS9 started out as a Trek series that seemed to want to break away from the double standard with female characters. Dax is a woman who is also kind of a man, and Kira is the butchest butch ever to be butch in the galaxy. I was like, "This is so cool! I can't believe a studio went for this." In the first couple seasons I felt like they were always given equal treatment to the male characters.
And then Dax went from being "one of the guys" to "Worf's girlfriend who spends her spare time at the bar and talking about boys," and after years someone woke up and decided it needed to be clarified that Kira is, in fact, a woman (I'm not sure why the Intendant wasn't enough proof), and suddenly she had heels and a skin-tight uniform, which by season 7 was no less insulting than Troi's or 7 of 9.
The early episodes with Dax and Kira going on missions together were a great step forward in Trek's depiction of women. It's frustrating that they were doing so well and then lost sight of it.