You are not getting the point though. Fiora dodges abilities that are thrown at her denying any damage while putting abilities on cooldown. While fizz only becomes untargetable and any ability thrown at him will not go on cooldown and you can activate it again. Also it isn't dot abilities that damage him during it, it is any ability that affected him before he became untargetable.
Sure it makes stand still but she cannot take damage. And it isn't for damage either. It is a skill that makes her trade very well in lane, deny cc, and dodge abilities.