Admittedly, Nina has had more time to develop the nuances between Elena and Katherine, BUT if you go back to season 1 -- it's obvious that even then she had developed individual voices, facial expressions, and body languages for both characters.

The fic I've been reading is leaning toward what you've said about the Hunter and the Witch but I'm unsure if this is coming from the books, spoilers, or speculation. IF the original witch is the Petrova or one of Klaus's family or even European how does that work with the current mythology of primarily black witches? So far all the witches/warlocks we've seen have been people of color except for that one white guy.