If the Genshin Fandom were even a smidgen less sexist, Dottore would be treated with the same scorn that Signora is treated with.
Say what you will about her, but Signora was consistent -- she was on a quest against what she describes as "the world's crookedness," and had a personal vendetta against Venti. And she not only did fight this injustice in the way that she thought made the most sense -- through helping The Tsaritsa collect the Gnoses -- but she also focused much of her fury on Venti, who proved her right by proceeding to be a major piece of shit and talk himself up and down, what, four years after her passing?
Sure, the Fair Lady was anything but to some, but every Harbinger who had something worth listening to spoke in her favor. Even Capitano, who described what had happened as Signora tarnishing her honor, called her loss a great pity! Sandrone and Columbina cannot stop talking about how good of a person she is, and the fact someone as principled as The Knave was audibly emotional over her passing shows that, at the very least, there was a great deal of sympathy for Rosalyne Kruzchka-Lohefalter.
Dottore is a lunatic who people only agree with because, from what I can gather, they want to have sex with him, and he is a man.
I am not going to just declare that Dottore has no point to make: He is not necessarily wrong in his claim that the divinity of Teyvat is a restricting force that has not allowed humanity to progress like it should have. In a world as vast and limitless as Genshin's, there really is no other explanation for why such a select few are powerful and limitless.
But it is also this fucking clown making that point. Sure, he is not wrong, but he is also the single least qualified person to be making that argument. Zandik is one of the two people in the Fatui we know to have had formal education, the other being Rosalyne, and he is the third most intelligent out of the two. He puts on a wet paper-thin guise of affability and intelligence to mask the fact he is a dumbass who experiments on children, frequently gets his colleagues and subordinates in trouble for no real reason, and only has any goodwill with the Fatui because the guy who gives everyone a salary requires his services, all the while bitching at The Traveler -- someone he should hate for being a kiss-ass to the same divinity that constricts mankind's progress -- that it is alright for him to bring serious harm to Nod-Krai and everyone there The Traveler holds dear by letting Rerir run amok because Nahida is a big fat meanie and didn't let him fly. He spends a nauseating amount of time bitching that humans cannot fly that even I, someone who loves Fatui motive rants, audibly groaned at how much of a whingy child he is.
And it isn't like he didn't have time to explain his motives in a way that could make the player go "well, damn, he's right" in spite of his cruelties. Signora, Scaramouche and Tartaglia are all textbook "evil Harbingers," yet all three manage to have motivations and beliefs that aren't diminished by how cartoonishly cruel and stupid they are. Dottore fans have to fucking misinterpret the game to pretend that the guy who traumatised Collei and had a deal with Crucabena to experiment on what is implied to be disabled orphans from the Hearth is being treated the way he is due to favoritism, to the point that I have seen some of his fans cry that Arlecchino has "ethical child soldiers"(?!) and gets treated better purely because she is a woman, as Genshin fans famously treat the female characters well[sic].
Why am I saying all this? Because, despite all the shit he has done on-screen, Signora is treated worse than Dottore. If you look at the conversations "serious lore fans" had about her, especially before Hoyoverse made it clear that they think it is fucking weird to hate Signora so much by showing that fan-favorites like Arlecchino and Columbina genuinely loved her, it is mostly psychotic ramblings about how much of a piece of shit cunt whore she is for kicking Venti and how she "deserved to be humiliated"(?!?!?!?!?!) for her opposition to The Traveler, who was horrified by her death, and Raiden Shogun, a raging fascist! She may have the most horrific misinformation spread about her in all of Genshin, which is an incredible achievement given that Genshin women in general have a nauseating amount of gross misinformation spread about them! People genuinely hate her for shit some rando made up far more than they hate Dottore for shit we know he did because we saw him doing it.
It can't simply be because she kicked Venti, right? I mean, almost everyone has "moved on," for the lack of a better term, from Venti, and he has had his position as Twink of The Month usurped far too many times to count by now for it to be his relatively small fandom to be the ones spearheading some cringy ass "agenda." It cannot be Shogun fans, because the Shogun technically "beat" Signora. And I sure as shit doubt that the harem-brained Aether fans are happy a tall "evil" woman is dead and not wrapped around their Potential Man's ankle.
So, the answer is simply sexism. Signora is a woman, Dottore is a man. No matter what awful shit Dottore does, hundreds of thirsty misogynists will line up to claim that what he has done is perfectly rational or "not even that bad," while declaring that Signora is a horrible mean bitch who deserved to lose her significant other to Venti twiddling his thumbs because he is Teh God of Freedumb and he cannot use all the power he claims to have to stop the horrible monsters and giant dragon terrorising his people and then get killed herself after being dared into a duel she was literally not allowed to refuse. Dottore dying after years of abusing children, killing a colleague, bringing grievous harm to Nod-Krai, fucking over his own subordinates and doing everything he did to Columbina because she didn't want to be his little sister once she found out how much of a monster he is, though? Tragic. He had a point! They hecking wasted a perfectly good character, dood!
And, before anyone tries to come up with some cope as to why all the hate towards Signora was justified, don't bother. I am not going to entertain it. Not after seeing how you lot treat ugly greasy men who are ten times worse.
