Re: "Kabuto can't use Edo Madara?" Don't be stupid to think Madara isn't Kabuto's Bi
And Hashirama was the reason Madara became that strong, Izuna was the reason madara is strong, Itachi is the reason sasuke is strong, Kyubi is the reason why naruto is strong, Obito is the reason why kakashi is strong, etc etc! =) I can go on and on and on with manga facts of other ninjas using other ninjas powers stolen or given! Doesnt matter, they became strong because anothers power! =)
Next; Im not talking about current kabuto. Kabuto in his prime is the best! Deal with it! With your logic; Itachi, nagato, all 4 hokages, past kages, gaara, Aye, Onoki Jman and others are irrelevant aswell since they are dead or sealed. Does that make them Weak or useless anymore???? Think about it...
But the shinobi you mentioned were already strong before. Madara was the Uchiha born with the most powerful chakra the Uchiha Clan has ever seen. First Uchiha to unlock MS along with his brother, and the first Uchiha to tame the nine-tails. Izuna and Hashirama aided him in becoming more powerful, but in a manner unlike Kabuto's and he was already the second most powerful ninja at that time to begin with.
The same could also be said about Naruto, Sasuke, etc. Sasuke unlocked 3-tomoe sharingan and could have unlocked MS by himself. Naruto is of the Uzumaki so he definitely had some potential too.
Kabuto is virtually powerless without the powers he acquired, unlike Naruto, Sasuke, Madara, etc.
Kabuto in his prime was still defeated since his weakness was Itachi as he stated in the manga. Any Uchiha with Izanami can defeat Kabuto. The same couldn't be said about true legends like Hashi, Madara, Saru, etc.
I will admit though, in Kabuto's "prime" (if you want to call it that) he could pretty much defeat anyone with the edo tensei army. But what about without?
Itachi's already explained all of this about Kabuto very clearly in the manga and why he ended up ultimately failing.