I do notice that a lot of people are using KA as apart of Itachi's arsenal. KA is not really something that should count in these hypothetical fights (unless you are proposing that Itachi's crow gets Senju DNA) for the following reason:When Nagato want to use CT, Itachi will using Amaterasu to disrupt him
Nagato can't just neglect the effect of Amaterasu or else he will burn to death
That mean he will react, when he react to absorb Ama from his body
Itachi will fire yasaka Magatama at Nagato to add second attack that nagato will absorb
And then Itachi burn the surrounding of Nagato to limited Nagato sight.
Nagato wlll try to escape from the fire by summoning his animal
Yasaka magatama again to the bird plus and Ama
itachi continue to using distraction base jutsu to limit nagato move
In his strategy to make Nagato trapped and close to him little by little
And then when nagato is in confusion, Totsuka stab him
Strategy is crucial here for Itachi
KA is also can be use and it will trapped nagato
Thanks
KA without Senju DNA can only be used once per decade. Therefore it is not apart of Itachi's general day to day arsenal. It is more so similar to the eighth gate, izanagi/izanami, reaper death seal, and Konan's 600 billion explosive tags in that it is a jutsu that is very situational (usually emergency only) and is not something that can be spammed or used regularly in battle. Therefore it does not count in hypothetical vs matches unless you are going to give the crow Senju DNA which shortens the interval to a mere few hours, or if you are saying that Itachi is just going to wait 10 years between every battle so that he can use KA.
Basically, if it can't be used regularly, then it doesn't count.
Furthermore, about the Kaguya thing from earlier: Even if Itachi works on his speed, chakara arms are pretty fast as well and they are long range. Therefore Kaguya could still destroy the susanoo from behind with chakara arms or even send the arms themselves through a portal and hit the back of the susanoo. Also, infinite tsukuyomi still easily beats Itachi (and unlike with KA, Kaguya can always use her 9T rinnegan).
Also, technically Kaguya could just warp Itachi to any dimension and then just go home and leave Itachi in that dimension to starve to death.