See, now, to me, that's a bit different. The writing isn't superficial - at least from what you're saying here. It's not, "Well, these guys are really evil, so, of course they keep slaves" sort of thing. Kinda like how the Red Wizards of Thay are written. Yeah, they're really bad guys right, so, they keep slaves to drive home that these are really bad guys. The problem is, all the writing is about the bad guys, making the bad guys really bad guys. Little space is devoted to the slaves, which are left more or less as a faceless mob.Actually, Paizo's Lost Omens Firebrands (coming out to the public in a few days) contains narrative exposition on how Cheliax has freed its slaves, but is targeting them with 'help' that creates horrendously exploitive binding contracts in ways that very much feel like someone was writing a fantasy metaphor for sharecropping or something similar. Now granted, it's still written from a very progressive viewpoint that this is a very bad thing the freedom fighters the book is about need to help fight, and I wouldn't be shocked if those passages were PoC written, but that is something that is going to be very personal to some people in the way that this thread is discussing.
By talking about the slaves first, or in this case the victims of exploitation, it's a lot less about how bad the bad guys are, and more about putting faces and names to the victims.
Not sure if I'm making the point that's in my head very clearly, but, I hope what I'm trying to say is coming across.