Number 2 is debatable. We don't know what the nutritional requirements for ball pythons are. For all we know, all the extra "nutrients" in rats may be expelled as waste. Gram for gram - there's no conclusive evidence that rats are better for BP's than mice. If you feed the same number of grams in mice as you do rats, you're likely going to have the same growth rate.
I raised up most of my females a few years ago only on mice. They were growing at a rate of ~100 grams a month on average. All of my adults are now on rats for reason #1, but not for reason #2. I have experienced no difference in the rate of growth when fed the same number of grams of prey per feeding, whether it was rats or mice.