@ part in bold....XD Kakashi was figured this out as well as how it works and how to counter it. I think you forgot the fight against Obito and the edo jins.
You make good points on the others. I am not trying to down play Madara or Itachi here. But no Kakashi's eyes stop going blind after he received the double Kamui Sharingan which is the Kakashi we are talking about here. You know the one who sliced and Kamuied the Rabbit Beast's arms/tail, Black Raikiri'd her with senjutsu from the Rikudo, and forced kaguya into her into defense.
Plot or know, it's still Manga fact that Kakashi took her on in this form. She is stronger than Madara, so does everyone think Kakashi can't hold his own against madara who isn't a rikudo jin in this scenario?
Kakashi never knew about the 5 minutes limit, he only knew Obito had to be tangible to attack and that their Kamui's are connected. Only Madara, Obito, Nagato, and Konan knew about the limit. Also Madara is a stronger fighter than Kaguya, he was only nerfed since Kishi wouldn't let him use wood clones, wood jutsus, katon jutsus, any Rinnegan jutsus (Deva, absorb ninjutsus, weapon path, summon), or his Susanoo. 1 Rinnegan Madara could have beat Naruto and Sasuke how they were in that fight with wood clones who can also use limbo, Deva path, absorb ninjutsu, share vision, and all of his jutsus but that would have beat them and never let the manga be where it is now so plot played it's role.
Kakashi wasn't fighting Kaguya alone and if you put Madara in that situation with Kakashi then TSB pierce PS making Kakashi go intangible, Deva path repel Kamui shurikens back at Kakashi if he throws them, absorb black chidori or use Deva path to stop Kakashi from cutting him. Madara, Nagato, and Obito (with Rinnegans) know how to use all chakra natures so nothing stopping them from using dust release or this black jinton like attack that Juubito used and Hiruzen said it had at least 4 elements and resembled jinton (dust release)
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