There is no proof that assure the contrary.
And... what about Sasuke? He killed Orochimaru and then revived him...

he surpassed his master too.
Killed a man on his death bed which was renowned as "The" evil genius in the Naruto universe, with edos at his arsenal, not naive, great body w/ the ability of continuous regen, etc.
He stands no chance. Another episode of plot no jutsu.
Orochy, is able to be revived because of his curse mark on many of his experiments.
He came out of Sasgey when he was vsing Itachi, who is to say he cant willingly do the same from other people with his curse mark. The man does not die.
I should have stopped at Edos at his arsenal. I don't see any chance of anyone beating a guy with edos [KAGE Level]
Kabuto could have taken down Sas/Itachi if his edos weren't away from him.
One might argue that he has the ability to summon them at anytime no matter the location, I agree and conclude that his death made no sense. He could have made Madara, and other past kages take them down for him while he just sits there.
Waiting on Sakura's new power to determine if there is two new Legendary Sannin's and not just 1.