I watched this movie yesterday morning and then yesterday evening caught part of Hacksaw Ridge on tv.
A movie like Hacksaw Ridge is supposed to have character development because it's about one man's experience in the hell of war. Its important to see the persons background and motivations and reactions through the event. And you do see the effect of that one event on the person. But almost at the expense of seeing the effect of the event in the grand scheme of things - i.e. the entire war and the nation fighting that war. In fact, many times in these type of movies, because of the focus on one or two individuals, you don't even see the scope of the entire event to its fullest extent.
A movie like Dunkirk is about an event - in this case a large group of people, in fact an entire nation. Not the individuals involved in it. Focusing on one or two individuals would have shifted the focus from where it was supposed to be - i.e. the British nation reeling from the Axis onslaught, some considering surrender, but then catching its breath, deciding that they weren't going to give up that easily, and fighting on. The "lead character" was the British army/nation, and there was plenty of development of that "character" if you watched the movie and grasped the point of the movie.