He's protected. But how long will he have to fight? Stamina would be important if he has to defeat hundreds of opponents.
But using Susanoo and Ama (two jutsus that tire him the most) at the same time would drain him a lot. Even a 30% Itachi was able to perform the said Katon without visible straining, but wasn't able to use either Ama or Susanoo alone, much less together.
Once Tsunade is dead this fight is over.
How many times am I going to have to repeat myself.
Tsukuyomi.
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Fire Style. (Twice)
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Large Scale Amatersu (Twice and Prolonged)
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And then Susanoo for chapters 392 and 393 and the beginning or 394.
Yet you think he will collapse and cough blood, from using 2 smaller scaled Amaterasu's and a lvl 1 Ribcage Susanoo when he was using a full lvl 4 one before? No, that doesn't make sense.
Not to mention 1 Tsukuyomi can just wrap this up quickly. Itachi's sickness is never becoming a factor here.