Even without the rinnegan, situation didn't change except for a six beast front of bijuus in his disposal.Itachi was busy with Kabuto while Obito had Rinnegan, you trying to even suggest a fight that couldn't have happened given the events and insinuating Obito would win is pointless. MS Obito vs. MS Itachi and its not even completely fair because half of Obitos body is Senju DNA
Didn't read what Madara taught him?
Neither had the rinnegan, with it....
It would be a complete stomp