Dear Friends,
An excellent series of posts on a sensitive subject!
Certainly, even if the Eastern Catholics held IDENTICAL beliefs about everything, this would not make them “Orthodox” since they would not be in communion with the Orthodox Churches. There is no sense of “hey, we believe as you do, so we must be as you are.” Doesn’t work like that in either Church.
Eastern Catholics today tend to resemble the Anglicans in terms of their “Eastern identity” meaning, “High Church Byzantine” and “Low Church Latin.” Despite papal pleas to be as Eastern as possible, there are EC’s for whom this is just not on their radar screen at all.
I am one of those who accepts everything Orthodoxy teaches but, undoubtedly, as a Catholic, I will see in Orthodox teachings a “Catholic inflection.” So if we say that the Holy Spirit proceeds “from the Father through the Son” (as Aquinas acknowledged as well) and say this is comparable to what the Orthodox teach - we would, in fact, be wrong.
“Through the Son” most commonly refers to the “Economic Trinity” and, in any evern, it is not a doctrine, but just a point that some Fathers bring up now and then. Does this term refer to the eternal relations of the Trinity? There is no Patristic evidence that this is so.
However, both East and West do agree that the Spirit’s “proceeding” is different from the “Son’s” begetting from the Father. And on principle EC’s don’t have the Filioque in the Creed etc.
That the Most Holy Theotokos never sinned in life - that is something both East and West believe and the East celebrates her Conception as a feast day, meaning that she was a saint at her Conception. Would Orthodox agree with that? Yes and no. But as an Eastern Catholic - I don’t care.

Sometimes, Orthodox teachers will bend over backwards to try and show how different their theology is from that of the RC theology when all it is is simply another way to understand the same thing - as has been well-stated by others here.
As for Purgatory, Orthodoxy doesn’t believe there are “places” for the reposed prior to Christ’s Second Coming when we will be reunited with our bodies.
From the Orthodox POV, it is the state of the soul that determines its fate in the next life, not any “place.”
The “mystic Fire” which is God’s Love envelopes all souls when they pass into the next life.
For holy souls, that Fire will bring blessedness and joy. For those souls who need being loosed from their sins (not unto death) or who haven’t performed works of repentance tec., that same Fire will slowly cleanse them with the aid, of course, of the Divine Liturgy and the prayer of the Church on earth. For those souls dying in willful alienation from God, that same Fire will prove a source of remorse etc.
But the East does not accept a “purgatorial fire” and the Roman Catholic side at the Council of Florence never expected the East to endorse any idea of a punishing fire in purgatory for the union to be effected.
One of the great failings of the Council of Florence on the Catholic side was that scholastic ideas and even unimportant arguments came to be a “faith standard” for the Greeks.
So the useless Scholastic arguments about “what constitutes the fire of hell” surprised the Greeks there and one of them told a Latin theologian who posed the question, “You’ll be able to find out definitely once you get there.”
Alex