A complex and well written rules set isn't necessarily bad, but warhammer is not one of those rules sets. It's just complex, even where it doesn't need to be, and inconsistent, unclear and ambiguous on a massive scale. The big difference between the two systems, for me, is that Kings of War, generally, doesn't have rules it doesn't need, and makes sure that the rules it has work as part of the overall rules set. It also makes a genuine effort to be as balanced as possible. Warhammer, by contrast, increasingly feels like it's been taking the opposite approach, adding complex and unnecessary special rules just for the sake of having more rules, with little or no regard to game balance or practicality. This difference is why I now play Kings of War instead of Warhammer. Because, as a game, it works.
Yeah the complexity of KoW comes out on the tabletop not on the list building utility. If all you care about is fluff it's pretty easy to just forge whatever narrative you want.