I think the fact that Discord is supposed to be a "soulless monster" is a lot more of a fancanon than actual canon. I don't think Discord deserves to be called that. He didn't ever kill anyone. He just likes to causes disorder. And I know this has been said a million times, but this is supposed to be a kid's show.
Well, this has been said before, but Discord is essentially Q, the character that John de Lancie played on Star Trek. He causes a lot of problems, but I wouldn't call him a bad guy. They both just have lots of power and choose to dick around with it. I don't think either on is heartless, they were just enjoying themselves.