Something I love about writing fanfiction is that when canon drops an absolute dungheap of a writing decision, you do not have to just sit there and be disappointed about it. You have a whole world of interesting options.
1) Nothing here is salvageable. This plot point is a trash fire and it’s quickly setting the rest of the franchise ablaze. We as a fandom have elected to ignore it. It did not happen. I will write events as if they continued correctly.
2) Nothing here is salvageable, trashfire, etcetera, but let’s just play in the space for a moment. If we allow that fine, this incredibly stupid thing happened, can we mulch it down and grow something interesting from it? What led to things ending up so off the rails? Where do we go from here? What are the worldbuilding implications? I will dig deeply into this dungheap and make something worthwhile out of it.
3) There is the seed of a really good idea in here. The execution was garbage, but if it had been done differently, with better writing, with better pacing, with more thought and care and tact, it could have been golden. I will redo it, but better.
And there are many interesting combinations of correct/worthwhile/better! I love delving into this in my own writing, and seeing it in other people’s writing, because suddenly your fic is having a conversation with the original work. It’s transformative! It says something about what you personally loved and hated and took away from the story!