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1- he 1HKO kakashi with tsukoyomi
2- he 1HKO orichi twice (once when he cut off his hand the second when he sealed him)
3- Almost made Deidara kill himself and he wouldve if he taunted him a little more.(also 1HKO btw)
Agreed
4- He defeated Nagato whos probably the second strongest villan behind Madara (imo) even after naruto and bee fed nagato their biju chakra and restored his health/youth.
You did forget to mention that the same people who gave nagato chakra, also helped fight him. Maybe itachi could take nagato idk, but i simply want to point out that he didnt do it alone.
5- he also defeated sage kabuto even with sasuke being a pain in his ass. Though i admit sasuke saved him once during the fight.
Want to point out, that they still did work toghther, and that both itachi and kabuto wanted sasuke alive. It is possible, that if sasuke wasnt there, that kabuto would use killer moves on itachi, since itachi is edo, he would regen, so say kabuto used a random move that hurt itachi bad, then while itachi is regenerating, kabuto could possibly regain control of him. The true question, is if itachi soloed, would he be able to land izanami, before kabuto could regain control.
Simply itachi didnt solo kabuto either, and both itachi and kabuto were holding back(itachi because he didnt want kabuto dead, and kabuto, because he didnt want sasuke dead).
6- he couldve defeated jiraya. even kisame was confused why itachi didnt.
Itachi is known for very good for understanding peoples powers strengths and techniques. Itachi knew much of how strong jman was, and so he with his expert skills in anaylsis understood that even with kisame, they would stalemate. Here is how it could work logically. Logically, kisame isnt as strong vs non jin, as a huge part of his strength, comes from useing the enemys chakra. So since jman is skilled, kisame would not be able to drain much chakra, makeing him not be as strong. Itachi has the opposite problem, as he has strong techniques, but low stamina. SO simply jman, who is known for great stamina, and endurance, would with his skills out last itachis, strong techs, and kisame would wear down as well. In the end they all collapse due to overuse of chakra.
7- if you noticed how kisame follows itachi's orders you would know that kisame is certain that he doesnt stand a chance against him. thats why he respects him so much.
Kisame may stand a chance against him, as he has samehade which could get kisame out of itachis genjutsu. After that they could fight pretty fairly. Kisame simply respects itachis insight, and strength. It doesnt mean that he doesnt think he has a chance against itachi.
8- not to mention that he killed the ENTIRE uchiha clan by himself without being scratched.
you dont know he didnt get scratched, and he had obitos help... Also it was a surprise attack as well.
add to that an EMS through sasuke's eyes plus those special weapons that he has on susano and he would be only matched by madara.
very possible
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The parts in bold and underlined, are parts that i answer. I am no true fanboy of any character, just of the entire series. I base my logic, off the proof in the manga. I try not to be biased as well.
Simply itachi was a beast op ninja, when he was a kid and when he had his illness. A healthy ems itachi would be very op.