See, I think the point that's being missed here is context.
Succubus or harpies, AFAIK, don't have a history of being used as stand ins for the "Other". There's no lengthy series of works in the genre where harpies are used at all, again, AFAIK. While there are stories with succubi, they are again, not seen as "lesser beings" ripe for having their property and lives taken from them.
Look at how vampires are depicted, particularly since the 80's. They aren't lesser beings. If anything, they're MORE human than humans. They are typically wish fulfilment fantasies filled with very powerful beings that can do whatever they please, whenever they please. Lestat being a prime example here. Or Spike from Buffy. Who wouldn't want to be one of those characters? Powerful, immortal, doing whatever they want, taking whatever they want, and always getting the hot girl.
Those are not negative depictions at all.
Now, picture orcs, or beast men, or whatever sub-human variant your fantasy du jour has. No one wants to be an orc. No one wants to be a kobold living in a sewer. Sure, half-orc is cool, or that kobold PC is cool. Because you get all the good things about the race - stronger, faster, whatever - and still get all the benefits of belonging to the "us". There's a very good reason Gully Dwarves have never caught on as a PC race.
The colonialism in D&D is hard wired into the DNA. It's undeniably there.