You Oro fans are persistent, like your fav character ill give you that.
However he bites the dust yet again.
1. Zetsu argument.
As somebody has said already the feats demonstrated by spiral zetsu and the common zetsu who got slaughtered like sheep are two different things. Even if we were to assume that the common zetsu gets the same feats as spiral zetsu obito, his mokuton feats still wouldn't pose a threat to Itachi or any kage tier ninja.
Another thing you forget is that the mokuton strength of spiral zetsu is determined by who it encases. Obito literally had a part of hashirama's dna slapped on him, but also had the uchiha strong chakra. That is why he managed those mokuton feat and that wasn't even impressive.
With yamato his mokuton even increased further.
What i am trying to say is that a zetsu body orochimaru encased by spiral zetsu still wouldn't have the mokuton strength of spiral obito or spiral yamato.
In mokuton it is
Hashirama > Madara > Spiral Yamato > Yamato > Spiral Obito > Obito > Spiral Orochimaru > Fodder zetsu Orochimaru.
His zetsu mokuton would not be greatly increased even by spiral zetsu as it isn't that strong to begin with. Its this very reason why he will not even be able to produce mokuton feats of part 1 edo Hashirama who's mokuton feats are still superior to yamato's. Likewise even if we give him part 1 edo hashirama's mokuton, it still isn't strong enough if you consider that enma was able to protect old hiruzen and but also destroy the trees. Replace enma with susanoo and its all game. Amaterasu will also have a say in this. If old hiruzen can survive edo hashirama mokuton, see no reason itachi cannot.
2. Techniques he already. Mute point. Apart from edo tensei which got taken away, we still don't know what other techniques he had. Regardless when he was defeated by orochimaru and left the organisation due to this defeat at the hands of itachi he had these techniques. On the same note Orochimaru admitted inferiority from that event where he had his full techniques. Lets not forget that his strongest technique which was the hydra has been defeated already so any lesser techniques that he had that was sealed away wouldn't pose as much of a threat as his strongest technique.
Orochimaru regardless of his 'upgrade' if you can call it that, still strongest technique is the hydra
Orochimaru bits the dust for the 3rd time with mid to high diff.
Scenario 2. Stripping Itachi of everything to do with his sharingan and only restricting orochimaru from zetsu or edo tensei is basically non sharingan itachi vs sannin orochmaru. He doesn't have the techniques to put him down in this form so oro takes it mid diff