I think highlander is very much like a more reserved version of Zarathustra. They both form strong opinions about things that have real-world relations and working predictions, but Zarathustra presents these views very forcefully, whereas highlander seems to show a more steady will. Maybe it has something to do with instincts perhaps? It makes perfect sense to me though that they would both be INTJ 6s.
Still, I really don't know. That's just the way it looks to me. If I'm wrong, someone should correct me here.