Necropolis or Castle (Which one is stronger?)

No matter how much I play Heroes 5, the Necropolis faction almost always loses, whether it's controlled by the AI, me, or a friend. Throw stones at me, but personally, I don't know of a SINGLE instance where people lost to the Necropolis... not a single one. Even according to the lore, Necromancers are not a fully-fledged race, but only descendants of mages. That's how it is.