[Theory] Invincibility in MS users/Yata
A lot of people say that Yata mirror isn't invincible because nothing is invincible. Well, we already have 3 characters that can become completely invincible against any attack: Obito, Minato, and Danzo. If even a guy like Danzo can survive any TBB, wouldn't it be a shame that the man who ended the Uchiha clan has no such feat?
it's not logically impossible that Yata is invincible. It could work in a similar way to Obito's intagebility. Yata probably forms a barrier in reality. For example, if itachi encases himself in Yata completely, he essentially exists in a pocket dimension just like obito when he becomes intangible from kamui. The difference is that for Yata, the dimension is much more superimposed with the surrounding environment. In Obito's case, he is somewhat superimposed with the environment since, 1) he is still visible, 2) there has to be a way to connect the bloodflow, brain signals etc to his body parts on earth.
This fits with my other theory: MS users generally have a feat that makes them somewhat invincible. Obito can survive any attack via Kamui/Izanagi; Kakashi can one shot anyone with Kamui; Shisui can one shot anyone with Koto; Amaterasu users can almost one shot anybody etc.
So would it be so surprising that Yata provides an invincible defense? It would not be completely op. It would work like Obito's intangibility; complete invincibility for a few minutes, then ended by exhausting too much chakra.