No what he meant was that when he is wielding yata mirror and the totsuka blade he is invincible, due to the spiritual weapons. Not meaning that Itachi beats everyone, just that no one can beat him as long as he is wielding those weapons.
The rest you wrote is just speculation.
Literal interpretation of BZ's words: Itachi is invincible with Susannoo activated.
Inference: if Itachi activates Susanoo with the weapons, a team of Rikudo, Kaguya, Juubi jin Madara cannot beat him because he is invincible.
Inference: If the sun hurled itself at the earth, Itachi would be sole survivor because he is invincible
Inference: Itachi cannot die of sickness or old age which Totsuka and yata are activated because he is invincible.
You do realise how idiotic that sounds
Interpreting BZ's words with due consideration of the context.
Itachi had just shielded Sasuke's attack with Yata showing the potency of the defense.
Earlier, he had sealed away the persistent immortal Oroxhimaru, showing the potenct of his Susannoo's attack.
BZ was affirming that with due considerations of these two abilities Itachi, as he stands in the battle, is invincible.
Inference: Sasuke could do nothing against him at that point because he was invincible.
You see how less idiotic that sounds?
Obito said Itachi being dead meant the Leaf was no longer off limits. He was referring to the deal he had made with Itachi concerning Konoha. Does this mean he feared Itachi would kill him. for attacking Konoha? No, because, prior to when he said this, he allowed Pain send Hidan and Kakuzu to the Leaf and he had already ordered Pain to go there. He was not afraid to do both things.
Obito said if he had not kept back secrets from Itachi, he would be dead. Doesn't make itachi stronger. Nagato lost to Naruto, not because Naruto was stronger, but because of the secrets he knew about Nagato. If Naruto did not know all he knew then he would have lost. Pain said that if Jiraiya knew his secret, he would have lost to the Sannin. So basically the difference in strength between Itachi and Obito is like between Nagato snd Jiraiya.
The only thing we can conclude is that Itachi, if fully informed and fully prepared, can kill Obito. The statement smacks of inferiority on Itachi's part since he has to prepare first.
