Well, in terms of female participation and female roles, there is certainly an obvious improvement TOS < TNG < VOY, but I think you should include DS9, since, IMO, it treated female character the best of all Trek shows - even if they were still numerically in the minority. Not only it had some great female characters, but for once their gender was not the thing that defined their characters
I disagree with this.
The post-TOS shows, including DS9, cast women in roles
just for the sake of having women, in an affirmative-action move. That's sexist and not progressive at all. No one should be cast based on gender, but that is exactly what they did.
Behr even admitted that there is no way they were going to do S7 of DS9 without adding another woman to the show, claiming 'we
need a woman on the show,' which is absolutely ridiculous and proves the aforementioned point. That is why Ezri had no purpose whatsoever for being on the show (completely irrelevant to the plot, and a counselor being senior staff who takes part in all the station decisions makes no sense). She was included on the show
only because she is a woman, and show's quality suffered dramatically because of it.
To really treat women better like you are saying DS9 did would require them to be cast not based on affirmative-action/filling token 'women' roles just for the sake of having women on the show, but rather casting women because they proved based on acting talent alone that they are the best persons for the role. No Trek show has ever done that.
TOS treated women best out of all the Treks shows because it is the only one that didn't give them undeserved roles based on affirmative-action.