Huh. What you're saying is true, but Winn strikes me as less holistically bitchy for some reason. Her bitchiness at least has a reason to it, namely pure self-interest and political advancement. And she did try to destroy the book of the Kosst Amojan at the end, so that would indicate that she wasn't entirely without a conscience...
She was behind bombing the school and brainwashed the young Bajorian Engineer into accepting the death penalty as the will of their god(s). What conscience?
On the other hand, it seems to me that Nechaev just seems to walk all over her subordinates and acts like a complete pain in the ass just because she can. It's not that much of a distinction, I know; maybe it's just my perception.
It's the military, she's an Admiral.
When does anyone in the military speak nicely to subordinates? People in the military are trained to be hard noses. When Sisko needed a job done from his subordinates, was he nice about it? No, he barked his orders and made his crew jump into action. There was a reason why the subordinates of the Enterprise were intimidated by Picard. Treks flaw at times is making the audience/fans forget that these people are soldiers and that orders and commands are rarely given nicely.
Being a hard ass is what earns you Admiral pips.