I agree with some of your points here, but a couple of times you seem to contradict yourself.

... gratuitous, pointless, ironically racist language

Ironically racist language isn't gratuitous or pointless. It may be a bad idea, but irony is a point. I think the problem with Jimmy's language is that the juice isn't worth the squeeze. I does matter that Bonnie is black, because it confirms that Jimmy's use of the word is meant as a shibboleth - his relationship with Jules is such (Jules knows Bonnie is black) that he can use the word, ironically, with Jimmy. Absent Bonnie, and perhaps absent Jules's apparent indifference to Jimmy's word-choice, Jimmy might be expressing disdain for black people, but he isn't. But, as I said, I don't care enough about Jimmy to justify that particular bit of business

Django Unchained is nothing but the n-word[;] ... it has gotten a cultural pass, I think, because it showed something Americans had never really seen before, and that was the mass, wholesale, unapologetic massacre of unrepentant white racists.

Django can't be "nothing but the n-word" and also include said something America had never seen before. In my view, the n-words in the movie are part of the justification for the massacre. The Southern gentlemen in Django use the word to dehumanize, and the drumbeat of it seems to me to make their unpleasant end feel good to the audience.

It's hard to picture the movie without constant reminders of the awfulness of those slaughtered. Yes we know they were awful, but a movie, as an artwork, is an emotional experience, and the n-word is part of that. The sins punished must be committed within the movie - not necessarily onscreen (although that is always Tarantino's choice) — but not only in the history books, either.

I can imagine Pulp Fiction without Jimmy using the word, but I can't imagine Django being sooo unchained without it.