The drop rate of animal fats is just too low to be able to level Candle Making after a while. I know there are recipes for filthy and lumpy animal fats, but I would think that it is intended for players to be leveling by grinding the higher level recipes. Afterall, after a while the lower level recipes give less xp or no xp.

I just spent a little over an hour running around in the Fae Realm killing fae bear and fae panthers, out of whom can give Typical Animal Fat on butchering. My butchering skill is maxed (82), as are "Bear and Bugbear Anatomy" (50) and Feline Anatomy (50). I have Yogzi's Butcher Knife, which gives and effective +3 to butchering level (so effective 85). I already know that fat is not considered an body organ, so Amatusa's Organ Knife doesn't matter, though I am carrying it as well. Most of the time I get 1 meat from the animal, so my count of meat is close to the number of animals butchered. It might be off by 5%.

This is what I collected:

Robust Beast Meat: 95
Robust Cat Meat: 88
Rib Bone: 19
Stomach: 17
Femur: 15
Heart: 10
Spleen: 10
Astonishing Animal Skull: 6
Brain: 6
Typical Animal Fat:4

Some of the stomachs were drops rather than the result of butchering. I would say 4-5 were drops rather than butchered.

Maybe make the animal fats a "rare meat", per the bonuses from the anatomy skills, so that there is a bonus to get them with the appropriate anatomy skill without the boost that body organs get from Amatusa's Organ Knife? I don't think that "rare meat" designation is being used for anything at present. If it isn't even coded for at present, then perhaps either having the animal fats be organs, or just tweak the % chance of getting them?