Your mistake is assuming that Barbara getting shot is "EXTREMELY IMPORTANT AND PIVOTAL" because of the audience's connection to Barbara. But it's not. That matters because it's part of Joker's ploy to break a man psychologically. But he fails. Gordon still tells Batman to do it "by the book." Yes, Gordon matters. Gordon in particular could be replaced with other people in Joker's point (that's the whole idea of Joker's idea: if Gordon can break anyone can), but IN THE ACTUAL STORY he matters. He is plot-relevant and thematically-relevant. Barbara is only significant insofar as she affects Gordon. And this is all a reflection on Batman's relationship with the Joker. You seem to think I'm ignoring what this means for Batman and the Joker but I'm not. In fact, in my last post, I said as much:>and how this plays into his relationship with Batman
The 'his' being Joker's, to clarify. I'm just capable of appreciating and understanding basic parts of how a story is setup and told.>Gordon could be replaced with literally any character
But that's wrong anyway. Having it be Gordon in particular helps highlight the thematic ideas that drive the story. In part because of Gordon's general characterization, but also because of his relationship with Batman in particular. It also helps that Gordon, like Batman, has a lot of history with the Joker.>BECAUSE IT IS A COMIC
So what? Storytelling is storytelling.