I think a lot of people think of goblins in a much different way than I do. They have a cruel streak in them, but it comes from a place of apathy, anger and boredom. I don't picture many goblins purposefully attempting to make their slaves/kidnapee's lives difficult on purpose. They would have to go out of their way to think of ways to do that. Their creativity is funneled into playing with dead bodies, or other very amusing games that don't require them to think about complex things such as the emotions of others. They're not good with understanding emotions in the first place.
They don't understand food, so when the people they've captured tell them what they need to eat, they should believe them and just think it's weird.
<Human> We have to grow vegetables because they're the most efficient way to feed everyone you want us to.
<Goblin> Whatever, just do all the boring stuff yourself. And do it good!
<Human> Okay!
I think Goblins need leaders from other races because those other races have a greater capacity to be cruel by actually understanding emotional cruelty on a higher level. They need something to aspire to. They need an "art level" cruelty to look up to that they can never seem to grasp without outside help. Humans, elves, and dwarves can do that for them.