Hildibrand actually shows proof of how dark the setting can get because every single thing in that questline is a direct result of how Ul'dah treated Sil'dih. Yes, it's shown in a very silly manner, and gets resolved rather peacefully considering what was about to happen - Still, you want proof of darkness? You got it.
My problem with that is essentially that even in NPC blurbs you barely see it. Even a throwaway line would be good, but they specifically go out of their way to not mention it. Other than for Duskwights in Grid, there's barely anything.
Ishgard is actually better in that regard in that it does showcase what the setting allegedly is (two young kids struggling to read a simple memo in the Jeweled Crozier showing that literacy isn't exactly a strong point, etc.) but in so far as racism is considered it's still not that very well shown.
I'm saying, he might have said it in a Q&A or something, but it's certainly not something that came up during discussions on what they should have NPCs say, or storylines, etc. Else it'd be there more often, y'know.
It'd certainly explain why Ishgard is actually showing how hard life is for the average Eorzean and the other cities aren't - it was developed after them.
To me, this whole "Eorzea's racist as fuck you guys" screams of "Dumbledore is gay". Something that was said by the author/someone prominent enough to make that call after the fact, that has absolutely no impact on the story in any significant way, that only serves to make a few people thumb their noses at others for not being on the hunt for every single possibly significant piece of lore ever.
And the most important part... Koji Fox said that? Source it. "Go look in the lore Q&As" isn't good enough.