I feel like there are three strands to it: romanceable characters being bigoted in ways that affect people in the real world, romanceable characters being flawed in other ways, or romanceable characters being rivals or hostile to the PC.
I’d expect something like a romanceable character being unrepentantly homophobic or like, constantly doing terrible things* to be questioned by the editors to see how the writer was planning to handle it in-game. I did a summary of the house style over here - it’s fine to depict bigotry if it’s done thoughtfully, it’s just that the narrative shouldn’t support/glorify it.
I can’t speak to depicting real-world bigotry in detail as it’s not something I tend to write about much, but in my experience, perfect/kind love interests absolutely aren’t something enforced by CoG/HC at the application stage - or ever! If all the romanceable characters were set up to hate the PC, I could see that raising questions about the risk of it being one-note, but CoG have always been perfectly happy with accepting pitches from me with flawed romanceable NPCs, or romanceable NPCs who are hostile to the PC. I’ve never had them give me feedback suggesting that characters should be nicer or less flawed, or that I shouldn’t lean into the characters’ imperfect or unkind aspects.
I do agree there’s a risk of romanceable characters becoming flatter if the writer is prioritising them being likeable/relatable/universally appealing though. I see this in other media too, but games (and dating sims in particular) can be especially tricky for this because of ending up focusing on perceived player wish-fulfilment to the detriment of rounded-out characters.
I haven’t experienced that with the CoG and HC games I’ve completed, though - perhaps I’m playing the wrong (or right) ones. Or I end up not playing until the end if the characters haven’t gripped me.
*although I will say: CoG never asked me to tone down Mayor Ferro from Blood Money, who’s a nasty piece of work who does various horrible things in the game, nor to dial back anything about some of the bad things some of the Noblesse Oblige or Honor Bound characters have done or do onscreen.