That's because glaring inconsistencies are present everywhere. Given Tobirama's prestige garnered by Sasuke, Madara, Naruto, and Minato, there's no conceivable way thatTobirama and this techniqiu AINT this fast. Kisame's clone or something like it, was fighting with guy, who is incredible fast and even bet him in taijutsu. As i remember. If tobirama was so fast and were able to kill kage lvl shinobis with next move : (throw marked kunai, FTG, slice someone in a half), why would he was killed by Ginkaku/Kinkaku ? It just aint make sense.
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to begin with. Tobirama was among the strongest shinobi during the World War and his feats and portrayal nearing the climax of the War Arc are literally incongruous with previous feats that Kishimoto mentioned. This is why the manga is analyzed holistically instead of cherry-picking feats because a holistic analysis is less prone to bias to begin with and we're capable of arriving to more rational conclusions via synthesizing information.
If we want, we can cherry-pick feats from Part 1 where Kisame would be visually depicted as weaker, but that's an unreasoned approach for obvious reasons.