Neji low diffs the first scenario and mid diffs the second.
That jonin title given in a time of war and struggle is not winning kakashi this battle , gai directly compared young kakashi to chunin prelims sasuke.
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Kakashi as a adult was in awe when he saw only a small sample of neji's power despite having recently said the hyuga were konoha's greatest bloodline and it was confirmed by hiruzen abd how the general public viewed the hyuga that they were a clan of expected genius and skill.
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Kid kakashi would have a hard enough time beating a rested chunin prelims sasuke who kept up with haku and orochimaru , same haku who was hyped by zabuza who kicked adult kakashi into prison to bein above his level and bein a very capable ninja.
Sharingan would able sasuke to see kakashi's jab and react to which kakashi who had no sharingan could not see the counter , ib4 kakashi fans claim he has lee speed so he will blitz , lee himself noted this
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The reason why his raikiri was incomplete in the first place , so kid kakashi loses to prelims sasuke who adult kakashi noted stood no chance against neji who only gave a sample of his power as noted by kankuro
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So kid kakashi gets low diffed when he decides to chidori blizt neji , cant see neji's lightning fast counter then bam!! Low diff
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Scenario2 : Neji will barely flex his powers and kakashi gets sent flying by kaiten sooner or later and when that happens kakashi will die mid diff since neji kept up with KN0 Naruto in a battle of speed , while adult kalashi noted that naruto's base chakra was many times the size of his own meaning naruto's speed/power in KN0 would be wayy above that of kid kakashi since naturaly more enhanced chakra activity would equal more speed/power/stamina , lee himself needed hidden lotus to bypass neji's reaction , kakashi stands zero chance in this battle.