Kishi is obviously preparing for naruto vs. sasuke battle. I mean, he's weakening them both down so they are even with power. Naruto vs. Tobi is obviously kishi's way of lowering his power so it's not maximum. Sasuke and itach vs. Kabuto is kishi's way of weakening sasuke's power so it's not at maximum. Through these battles, kishi is revealing hidden secrets that have clues such as:
Zetsu's history. The fact that zetsu was created by Tobi and, is more plant like than human, that Tobi can grow multiple zetsus, and that zetsus grow from hasirama's power shows that Tobi knows a lot about senju, has done multiple experimentations like orochimaru, and has a greater master plan than project tsukynomi.
Madara knows Tobi's true identity. When Kabuto was talkin' ta Madara,Madara asked somethin' like 'is it him?' or 'is he doin' this?'.kabuto also knows Tobi's true identity too becuz he said yes. Tobi is definitely old and not young becuz during his battle vs. konan, konan blew off part of his mask,showing his right eye with wrinkles. I only think that Tobi might possibly be obito becuz obito gave his left eye,and Tobi only shows his right eye before he got rinnegan. He most likely could not achieve it, or y else would he take it from Nagato? If he really did give to Nagato,then how did they know each other b4?
Leroy, I agree that yes uzumaki have high stamina,but the fact is, it's not only wen uzumaki and nine tails are together they r in harmony. Naruto had not befriended nine tails yet yamato's wood poles grew. Naruto and kurama worked better together wen they became friends.
Yes,maybe Kabuto has not achieved full snake sage,but that is highly unlikely being shown his abilities. Kabuto's histor py will play a role, becuz kishi puts these things in for a reason.