But still, since we don't know what Ball Pythons actually require nutrition-wise, what does it matter if a rat is bigger than a mouse, has more meat, has 15g of protein versus 12g, etc... If a Ball Python only requires 2-3g protein every week to maintain its energy requirements.

Like I said in a previous post, it's the weight of the prey item that should mainly matter, not the species. 2- 25g mice are the same as one 45-50g rat. Balls don't need a 400g rat every week to maintain, and would more than likely look at it and be scared, or they would eat it and fast for the next month.