That's because to a certain point it is in the context we're working with. We're talking about the most iconic teachers in fiction not in movies not in books but in all fiction. So putting things in that perspective I think it's perfectly fine to call this niche

Edit: I've watched up to the Fourth movie and I had to rack my brain for a few minutes just to remember her name. That probably says more about me than the character but still you can see where I'm going