Is Naafiri weak?

I'm rather new to playing Naafiri, and I've noticed that she feels quite weak, especially for her winrate. Laning is fine, but when it comes to teamfighting, no matter my strategy or build (assassin, bruiser) I just cannot manage to carry a single game. It is very frustrating to lose games simply because I'm not playing my other champs (like urgot, rumble).