I'm writing this as a reblog cause even though I've left this fandom, what you mentioned is half the reason why and I wanna shit talk these idiots.
Sadie doesn't get hate cause most people read her an unrelenting badass and a "girlboss". While the woman is also depressed, suicidal and hellbent on revenge with no care of her well being. Their reading of her is very surface level but that's a whole other story.
She's also conventionally pretty, so add some leniency points for that too.
Also, if anyone in this site ever went for Sadie, they'd be eaten alive by the gays and bis.
As for the others, most of the hate I've seen actually comes from people that revere their "love" interests.
Abi gets hate cause she actually has a backbone and doesn't just accept John's bullshit despite her love for the man. She's dealing with someone that at the beginning of the game literally says he wished he had killed her! and still stands her ground long enough for him to realize that he was being a grade A asshole and start mending his ways. But John fangirls apparently don't get that half the reason John strives to be "a good man" are his goddamn wife and child so boohoo, Abi's a bitch. When she's literally the one that pushed John to grow into a lovable and worthy character.
Molly's hate? That's straight up victim blaming. She left a life luxury and riches to run away with Dutch. She literally sacrificed everything for him. Left her privileged life, left her family, left everything for him.
But its her fault, somehow, that Dutch treats her like a fly, like a stranger and a nobody.
When he got bored of her, he just ignored her like she was nothing while he hit on the child he helped raise (Mary-Beth). But nah, Molly's the monster in this relationship.
Also, I might be wrong, but it wasn't Molly that ratted them out to the Pinkertons. She was so lost and fed up that she just wanted to hurt Dutch in anyway she could. And she hoped that saying she was the traitor would hurt him. As if.
I really wish the Dutch apologists never meet a man like him IRL cause if their take about the fictional characterization is that he did nothing wrong and his treatment of his "partner" is in any way justified, their lives are going to be a living hell with the real thing. Trust me, I have firsthand experience with the type.
And Mary? Half of Mary's story is every fangirl's dream. Fall in love with an outlaw? Be asked to join him in a life of freedom and crime? That's one of the most common fantasies. But Mary refuses it, because she is written like an actual human being with worries, a family and an actual life, and they can't stand that. They can't stand that a fully developed character isn't there for them to use as a self insert. So she is manipulative and playing with poor ol' Arthur.
When every time she asks Arthur for help she has exhausted every other resource she trusts, and at the end it is made clear that she still wants him romantically. She's the one that asks if they still have any hope together after their date, but Arthur needs to save his family from Dutch so he ends up refusing her.
The Abi, Molly and Mary hate is coming mostly from fangirls that want to bone their favourite outlaws and are so horny that have no critical thinking braincells left.
Also some gamerbros, but misogyny and victim blaming is the default for these asshats so I barely felt the need to mention them.
Anyway. Sorry for the rant.