When Blizzard said "Hero Class" they never had any intention of saying a class is more powerful as if you were a hero. It just means a class is more unique in play style. The word hero often seems to confuse players to think the opposite of what Blizzard defined it as. "It's also important to keep in mind that even though the death knight is a hero class, that doesn't mean it is more powerful than the other classes, just that it will offer a very different playing experience." — Quoted from the official Q&A on Death Knights.