Her damage isn't her weakness like they stated (dunno what their definition of 'low damage' is), but it is very evident she does have weaknesses.
I've yet to lose to a Zatanna online. Im just average at this game, so i tend to play other average players- but that shows Zatanna is not the kind of character any player can pick up and be good with quickly. We'll have to wait to see how good a character she really is.