Well the amazing thing is that you are trying to "be proved wrong" when you are just cherry picking a miserable portion of a miserable show with one of the worst MC in the whole history of cartoons, one that the author herself declared was going to be 99% about MC AKA Star.
Did you even know that Daron had created and developed the show about noone else but her? She even repeated it on many of the fucking interviews she had "Star is a girl that can and will do things by her own, alone."
Literally she was the only character that Daron had totally "developed" the rest, ALL OF THEM, were mere background characters and that included Marco, all she had was "he is a DBZ fan so that Star and Sol are like enemies", this meant that the team in charge had to think and develop them, unfourtunately they didn't have much to work with.
Jackie in those minutes of talk during their date showed small glimpses of a personality that could have been worked, but as Bisignano said, they literally focused on "Star's story" and decided which characters to develop and which not.>She was into history books, which could have been cool if they kept as a trait and kept her around. Imagine if in season 3 Jackie ended up knowing a lot more about Mewni's history than Star.>Liked Mellow music, no specification, so I'm guessing Jazz, some melodical, maybe even "ocean" music.>She wasn't quick to asume stuff or reject Marco when he began saying tons of embarassing things about himself.>She showed to be quite touched by his confession as to be ready to not care about how terrible the school made the dance night, knowing it was not his fault and wanted to actually try a relationship with him.
Meanwhile we have a MC that showed to be an autist that was too spoiled by her princess status so much so that she even did the "bitch move" declaring in front of everyone was not a "I'm never comming back" move, she knew they had ways to open portals. It was to damage their relationship.