Ok they're not black, but Zerrikanians are PoC, it looks like black people are from the other dimension that Ciri went to.
Yeah they count as poc and i get what you're saying in regards to the treatment of dwarfs, mages etc but there's nothing stopping them from creating black characters & other poc who are not an opposing threat. Still the witcher 3 is one game and this goes far beyond that.
Take Vivienne from DA inquisition as an example (another fantasy game), she wasn't the enemy but rather an ally (let's not forget some guards of the Templar.) It can be done but it's up to the game developers to have a more open mind when conceiving ideas and creating "fantasy" worlds.