That same kishi said other uchiha's used it in the past, hashi dna just prolongs the effect, but it's not among the qualificationsAsk kishi bro I didnt write the manga.
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He wrote that Kabuto fight well after this and created a plot hole just for Itachi to win with an asspull move.
He did'nt have intel on izanami + the uchiha bros did counter his moves, it's not like he had an op technique he did'nt useHe had all the intel on Itachi; Sage Mode; Sound 4 abilities; along with Hashirama and Orochimaru cells. There was no reason he should have been defeated the easily.