Here is my breakdown of the Covenant.
Grunt- One of those kids that your parents make you play with even though no one likes them.
Jackel- Those lonely geeky kids that hang out with each far away from others.
Elite- The cool kid at school that everyone looks up to, and respects.
Hunter- The big kid that protects the "small people" in times of crisis, and pays no attention to them afterwards.
Brute- The kid that always hangs around the cool kid.
Prophet- The old creepy guy that always asks you if you want candy.
When you put it like that, their genocidal campaign almost doesn't seem so threatening :)