How can Itachi win? He's not Amaterasuing a speedy FTG user. He's not landing totsuka blade on a FTG user either. His katons aren't beating Tobirama's suitions either. If he Susanoo camps, he gets outlasted and dies. Tobirama has already killed an MS user also. Tobirama has to be favored here.
Tsukuyomi, its genjutsu is instant and it's a one shot kill for those who don't have a Uchiha kekkai genkai or a sharingan to bare little resistance before collapsing slowly into the individual's demise (like kakashi). Tobirama has never encountered a Tsukuyomi before.
Susanoo keeps from ftg from hurting the user, so ftg slash is pointless.
And he isn't marked so all the better. Even if he did get marked, just like Sasuke and Obito proved they can remove the ftg mark since they had intel. Given itachi's genius, he'll figure it out.
Tobirama has only gone up against two ms users before and that was Madara and izuna, and during that time he was unable to kill either of them I. Battle despite having ftg. He had to wait it out until izuna was shown displaying a 3 tomoe sharingan to be taken out.
Ms doesn't mean Tobirama wins, otherwise Tobirama would've killed Madara before Hashirama did.
