In a large scale scenario, going beyond just the city, the elements of Destiny win over Warhammer. I will admit that Warhammer has many forces, factions, and powers that can stomp on any Destiny faction, the battle of the Light and the Dark goes beyond everything in Warhammer. The two powers are representations of life's complexity and Death's simplicity. If we bring just those two powers into Warhammer, a race far worse than the Hive would pop up slaughter half the universe and force the remaining half to join forces. But if we brought everything from Destiny into Warhammer (species and respective technologies) many of Destiny's races would be rendered extinct and the people of the City would scatter across the Imperium of Man just to survive. They would survive, they would adapt and they would become stronger.