I said he COULD kill Oro, not that he WOULD 100% no questions asked in a hypothetical fight, that's just ridiculous. No one ever said Itachi beat Oro in Akatsuki, we don't know that.
I think it's this inferiority complex of Oro's...he's so jealous that Itachi has a tool like the mangekyou sharingan that he's putting more value into the doujutsu than perhaps it even deserves.