Is sugar the main nutrient in a mango?

If we are talking about macronutrients, as in carbohydrates, proteins, and fats, then yes, I think it is proper to consider sugar the main nutrient in a mango.

One-hundred grams of mango contains around 15 grams of carbohydrate and about 13.5 grams of these are sugars, with only 0.85 grams of protein, and 0.35 grams fat.

Obviously, we have a lot of missing grams here. The rest is water. Like most fruits, mangoes are mostly water. One-hundred grams of mango contains about 83.5 grams water. If water was a nutrient than this would be, by far, the most abundant one.