Reasons/ explanations guys?
1. Itachi Katon is countered by Tobirama suiton.Itachi Suiton jutsu are countered by Tobirama's own suiton jutsus
2. Amaterasu is Itachi's fastest attack. As we saw in manga Tobirama already had knowledge about Amaterasu before Sasuke used it and Tobirama can easily react to it because :
- he can sense it coming just like Nagato and Obito did
- Raikage was able to physically move away form AMaterasu, Tobirama only needs to mentally react and use FTG to teleport away instead of using shunshin which is slower way of avoiding than FTG teleportation
- Tobirama based on feats has better reflexes than Minato and Mianto and Raikage reflexes were on same level as said my manga.
3. Tobirama knows very well about uchiha Sharingan so he knows that he needs to avoid eye contact .So Sharingan genjutsu or Tsukuyomi is never happening.
4. Itachi having Totsuka doesn't matter because even regular susanoo sword is enough to kill Tobirama .
Gaara with his sand was reacting to Susanoo swords, Hashirama was reacting and creating wood constructs to defend against Susanoo swords.Tobirama has superior reflexes than both Gaara and Hashirama and FTG is faster than Gaara sand or mokuton so he easily can evade Susanoo Totsuka sword.
- Tobirama can react with FTG to any attack Itachi can throw at him.
- We know he was using Gojo paper tag explosions before with his edo tensei so he will use them to nuke battlefield and force Itachi to use Susanoo as defense.
- Itachi trying to seal Edo with his Totsuka blade is useless because Tobirama will mark his edo with FTG an teleport it away every time Itachi tries to seal his edo
Tobirama has vastly superior chakra reserves than Itachi who has low levels of chakra and will constantly feel pain from Susanoo usage.So battle will come to the point where Itachi will no longer be able to use susanoo leaving him open for Tobirama to easily finish him with FTG slash.
In the end what matters the most Tobirama has way way more real combat experience. He spent half of his life in war. On top of that he spent that time fighting Uchiha's.He had more knowledge about Uchiha and their Sharingan abilites than Sasuke. He already killed MS user Izuna.
Tobirama is very intelligent so combining that with his battle experience and way superior stamina he wins this mid diff.