If Kabuto was able to revive every single significant person who has ever died before, why did he just wait until now to do it? The plot of this has gone to hell, but at least we might get some good fights out of it.
Also, Haku might get annihilated because of how powerful he was way back when compared to how people are now, but Zabuza at least was able to hold his own against Kakashi, so hes powerful enough to not be a push over.