Kabuto could only use Impure World Resurrection while having Orochimaru's DNA. We do not know how well Kabuto would be able to control all those summons on the same time, and the only one to be able to give Hashirama is a challenge is the summon that was enhanced by Hashirama's cells ---> Madara is only as strong as he is thanks to Hashirama's DNA twice. One for wood release, the other to unlock Rinnegan. On extention, Nagato and Obito also have Madara's Rinnegan with Obito having Hashirama's cells.
Hashirama is the strongest self-reliant ninja in history. The god of Shinobi. He doesn't need anyone else's cells like Madara did. They need HIS cells. He is so strong that you rise in rank just by putting his cells on you. I mean, he got Sasuke to soil himself in this chapter. Naturally without any outside sources as power ups, no one can match Hashirama. Even Orochimaru refers to him as a god, when he does not praise guys like Madara.
So we got a guy who could basically create tailed beast level creatures out of nothing. Creatures strong enough to stop Kurama, and to use a freaking Beast Bomb as an object! Surely the manga has stated Madara has access to the full power of Wood Release, but it doesn't mean he magically has the same level of mastery or chakra capacity Hashirama has.
Hashi has no way of knowing of Itachi's power. He is just stating that Itachi sacrificed more for the village.
