The dogma, as formulated and defined by the Roman Catholic Church, is incompatible with Eastern (Byzantine) theology, mostly because it explicitly mentions "Original Sin" and even calls it a "stain".
But if you ask an Eastern Christian to describe what they believe, they probably won't use those terms (yeah, some will.)
Fun fact: the Niceno-Constantinopolitan Creed, when recited in Greek in a Roman Rite Catholic Mass, omits the "filioque" because you can't correctly translate the Filioque to Greek. It would sound like a heresy. It's not a heresy, however, to omit it!
When we refer to "the Eastern Churches" we typically mean it in a very inclusive sense: every Christian Church which is one/holy/apostolic/catholic and not Western.
So we include the Church of the East (and the Assyrian/Ancient/Chaldean communions), we include the Oriental Orthodox (e.g., Coptic, Ethiopian, Armenian, Syriac, et. al,) we include the Eastern Orthodox Churches (autocephalous, in communion, celebrate the Byzantine Rite), and we include the Eastern Catholic Churches (which have counterparts in every other communion I already mentioned.)
That is Eastern Christianity, and in their traditional patrimony and theologies, which are diverse and formulated in different languages, they do not subscribe to "Original Sin" or the "stain on the soul" model. So, if you present them with the formulation as written by Blessed Pope Pius IX, they'll say no thanks.
Yet all the Eastern Churches agree that Mary is sinless. They agree that Mary is all-holy (panagia). They agree that Mary never sinned, before, during, after birth, during her life, and that she entered Heaven with body and soul intact.
So IMHO, the East agrees with the West in substance, but not in form.
The Eastern Orthodox Churches, typically, will deny that they accept any such thing that comes from Rome (the Immaculate Conception is a novelty, they say) and they will deny that their doctrines agree with Catholic doctrines.
Roman Catholic reputation among the Eastern Orthodox was repeatedly damaged as Catholics invited the corporate conversion of whole parishes and eparchies to become Uniate. In the United States, Roman Catholic bishops gained a poor reputation as well: read about Alexis Toth, Cum data fuerit, and the founding of the OCA, which was, basically, composed of Catholics.
>Yet all the Eastern Churches agree that Mary is sinless. [..] They agree that Mary never sinned, before, during, after birth, during her life, and that she entered Heaven with body and soul intact.
Not a dogma in Orthodox Christianity.
>So IMHO, the East agrees with the West in substance, but not in form.
You don't seem to care to make distinctions between Eastern Catholic, Eastern Orthodox, and Oriental Orthodox, so maybe that's why it seems so to you.
>The Eastern Orthodox Churches, typically, will deny that they accept any such thing that comes from Rome (the Immaculate Conception is a novelty, they say) and they will deny that their doctrines agree with Catholic doctrines.
Correct, Eastern Orthodox dogma does not give Mary's birth special theological status. So if you want to refer to Eastern Catholics rather than Eastern Orthodox, you should do that rather than arbitrarily ascribing your beliefs to other denominations.
https://www.ewtn.com/catholicism/teachings/pius-ixs-ineffabi...
Yet all the Eastern Catholic Churches have accepted the underlying dogma; they've even named parish churches after it!
https://icshrine.org/
But if you ask an Eastern Christian to describe what they believe, they probably won't use those terms (yeah, some will.)
Fun fact: the Niceno-Constantinopolitan Creed, when recited in Greek in a Roman Rite Catholic Mass, omits the "filioque" because you can't correctly translate the Filioque to Greek. It would sound like a heresy. It's not a heresy, however, to omit it!
https://branemrys.blogspot.com/2005/04/filioque-but-never.ht...