I think the main thing is to understand why oatmeal works: soluble fiber and the gut bacteria feeding on the carbs. That can be achieved within many other diets too. I wish they were more specific in saying what's special about oats, if anything. I also get upset when I see a ton of junk options at the grocery store. They are talking about plain cut oats and whole fresh fruit, but based on the way shelves are stocked…
I don't see how. Adding sugar doesn't remove the fiber.