Rats and mice are close to the same fat content
I have 2 female asf eaters that eat 25 gram asf's 2-3 times a week most weeks and are both about 1500 grams at 2 years old.
Mice and asf eaters can achieve the same weight gain as rat eaters but the key is husbandry and feeding often or multiple meals.
Given the proper husbandry most ball pythons will eat well and gain weight well no matter what prey type you feed them.