Mob Drop rates seem ususually low

I have recently been making/modifying some farms and i have noticed the drop rates for certain mobs being unusually low. For example the Zombie pigmen have dropped me over 10 stacks of rotten flesh which makes sense to he time i have been farming them. But they have only dropped me about 50 gold nuggets and 3 ingots. This appears astronomically low to me. Also the blazes dropped me around 15 stacks of blaze rods to only 2and a half stacks of glowstone dust. All of these tests were done with two looting 3 swords one old one and one new one to see if that changed anything.