Prime Obito? Prime JJ Obito with DMS? Oh lord how Itachi would suffer...
If a sick, diease-ridden, blood coughing, half blind Itachi was called Invincible by a old ancient black being from Kaguya's time, I don't even know what Prime Itachi would have been capable of….
Then we have Obito who already achieved his prime (JJ Obito) but failed like a fodder as usual
Do the math
BZ didnt call Itachi invincible he said the Yata mirror was
Its debatable if Obito's prime is his time as the Juubi Jinchuriki w/ a rinnegan or DMS Obito with Rikudou chakra
In any case Itachi looses against both