All the situations you described indicate valid reasons for a writer to edit their work. However, if we had to choose one that particularly emphasizes a significant need for editing, it would be Gabriel's situation.
Gabriel realizes that his entire conclusion is weak and confusing for the reader. A strong conclusion is critical because it leaves a lasting impression on the audience and ties together the main ideas of the work. Editing a weak or confusing conclusion can significantly improve the clarity and overall effectiveness of the essay.
Thus, while all the scenarios represent editing opportunities, Gabriel's case highlights a more pressing need for a thorough edit to enhance the overall coherence and impact of his piece.