I disagree with Jiraiya, Onoki, Orochimaru but yea almost 20.
A top 20 shouldnt be about the people who can beat him but rather who would rank higher than him overrall,,,, while you think Gaara beats him, it doesnt mean Gaara beats everybody Itachi is able to beat, which means Gaara isnt considered stronger than Itachi in the ened just because he could beat him according to you.
Either way, here's for you:
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Kishimoto clearly expressing his thoughts regarding Nagato and itachi's power on the side text
Nagato and Itachi are the strongest Edo tenseis outside of Madara himself, meaning the previous Kages, including Muu, are not considered stronger than them.
If Muu is able to match and defeat Itachi in a one vs one, which i dont believe is the case, he is still not considered a stronger shinobi than Itachi.
Just for the hell of it, The 4th raikage was going for a mutual strikedown against a ''not mastered'' version of Sasuke, who was not on Itachi's level at all yet.... Itachi beats him for sure
Gaara looses
Gai goes for mutual strike down
Kakashi looses
Tobirama looses
Onoki looses
Jiraiya looses
Bee looses
Muu looses or at least isnt stronger than him according to Kishi
Third Raikage would fall to genjutsu
Et prepared Oro Wins, but thats with preparation.... somewhat unfair but ok
Kabuto may or may not, hard to tell
Minato ties imo...
Here are the people i see being stronger than him
Hashirama
Madara
Naruto
Sasuke
Obito
Kabuto (ties/debatable)
Nagato
Minato (ties imo)
Gai could be in that list, but he needs AT LEAST 7th gate..... nothing less will make it
Itachi still makes top 10, far from top 20