the problem isn't urban fantasy or lack of brand recognition. the problem is making an rpg that isn't faux medieval fantasy. anything outside the world of wizards and castles is considered a risk. and, frankly, it is. the audience was raised in a very specific cocktail of early modern and fake medieval aesthetics and it is rather unwilling to let go.
I don't quite agree with that. If your game is good then people will like it. I mean, Kingdom Come: Deliverance and Disco Elysium turned out to be mainstream successes. If you make a good game set in urban fantasy I am sure people will like it. But it has to be good on its own merits.
The key operating words here are mainstream success. KCD and Disco are not jockeying for the forgotten realms audience. They transcend the pure rpg audience by default. A better case study would be Shadowrun. As far as combat rpgs go the Shadowrun trilogy is rather garbage. As far as settings go it is non standard in both ways: not only futuristic, but having elves in the middle of cyberpunk should be enough to weird out more than one buyer. And yet it was all successful anyways. So it's not impossible to succeed outside of realmesque, you just gotta appeal to the wider normiedom than the normies who mostly play rpgs.
Yup. This is why the pitches I'm preparing for urban fantasy try to maintain a sense of familiarity by recapping established genre tropes. It's basically the world we live in now but the paranormal is real and lives in a secret underworld beneath our notice. And it's more neutral, comedic, and campy in tone rather than "crawling in my skin!". Sure, there are vampires, werewolves, succubi, mummies and whatever that prey on the innocent, but there's also angels, slayers, charmed ones, and brooding vampire detectives running around fighting the darkness with witty quips.