James Cameron was the driving force behind the story in Dark Fate. All of the big decisions that so many people hated were his.
They had a team of writers, but regardless, if Cameron directed Dark Fate I'm certain it would have been much better than what it is.
But the things that people complained the most about - John's death - was a Cameron mandate. If I'm not mistaken, Carl's development after that was too.
Also, while there are about half a dozen credited writers on Dark Fate (and even more uncredited), more than half of them didn't actually touch Dark Fate's script. Most of them were part of the initial writers room, alongside Cameron and Tim Miller, that broke down the overall arc for the trilogy.