Whey is not magic. Whey is just, slightly expensive, convenient and very easy to prepare type of food in powder form, liquid after you mixed with water.
With / without whey at 2800kcal, your result will have no significant difference.

You already have the numbers, fill up the number with real foods, just that simple. Regardless what you eat, you need to fill number. You can eat ice cream all day, but I doubt you can hit the numbers. We don't do that not because ice cream is "magically" makes you fat, it just don't fit into our numbers.
And it will bring health issue cause of the refined sugar and preservatives, but isn't related to growing.