There is a lot of debate about high protein diet but all research shows that it does not cause kidney damage. Low protein diets however are beneficial to dogs who already have kidney problems.
If you look at dog's ancestry and wild dogs today, their main diet is made up of raw meats, I like to think of dogs as opportunistic carnivores, ie their primary diet consists of meat but when needed they will eat vegitation. That is at least, how wild canids are.
I would think a low protein diet would be recommended for a dog effected by fanconi but im not an expert on that.
Edited to add that kibbles without a lot of fillers are not always neccessarily high in protein, you can get kibble with more moderate protein levels but have healthier ingredients (ie not random corn and rice products, but grains that can be beneficial for example normal wellness)