I think your distinction between writing and editing is a little disingenuous, unless you're suggesting the editing was done by someone else. Editing is a part - some might say the most important part - of any writing process, and unless you think great writing is supposed to - or can - emerge fully formed in the first draft, then great writing presupposes great editing. And
Gatsby is one of those novels whose construction, from phrase upwards, never strikes a jarring note (at least for me, and most of the people who have written on the book), so it is by definition beautifully written, because it leaves no room for improvement.
The story being boring is a matter of taste, really. And obviously a lot of books get bludgeoned into boredom by being taught or over-taught in school. Like
@Jippy, I didn't read it at school and loved it when I first picked it up.