You ask if our average parishioner would understand this hymn correctly. I most absolutely do. Our parishioners are constantly attending the services of the Church. They love them: cradle and convert alike.
It frankly is impossible to regularly attend the services, hear the hymns and prayers in their full context, and come away with the idea that the Theotokos and the other saints are being worshipped and put on a level with God.
I seriously doubt that our churches would be filling with converts from conservative Protestantism if they believed that the Orthodox Church was saying by this hymn that St. Aquilina is "all-glorious" in the sense that she is as glorious as God, that she personally "glorifies us on earth" by her own power, and that she personally "makes us partakers in glory."
And as to the cradle Orthodox -- well, we converts learned our understanding of these things from them... I think that the most simple Russian or Greek peasant hearing the words of these hymns knew that Jesus is God and the Theotokos isn't, and interpreted the hymns in that light, just as we do today.
There have been a few converts, particularly some of the early Evangelical Orthodox, who wanted to change the ancient language of the Church in this regard to make it more acceptable to Protestant ears, but fortunately, they have been roundly ignored.
I don't for a moment believe that any even "marginally" Orthodox believer would for a moment think -- based on the teaching of the Church -- that Theotokos is anything even close to God, but rather a model human being.
But the extent of veneration that sometimes borders on worship, at least in the language if not in the intent, and the whole Marian devotion -- even her assumption -- is not something that can be easily glazed over and not detect that Mary's sainthood and veneration were neither part of the primitive Church's phronema, nor internal or external teaching.
Saints in the early Church were only martyrs. To the best of my knowledge none of the 2nd and 3rd century Fathers called her a Saint, nor did any one of them mention her assumption. Jesus Himself never called her His "Mother" but simply a "woman." One can speculate as to the cultural and social makeup of the male-dominated patriarchal Jewish society, but shouldn't we -- in the fashion of our Lord -- call our mothers "woman?" Rather this custom, revealed in the Scriptures, is ignored in our society, thus one begins to wonder which custom was selectively retained and which selectively discarded.
Customs in themselves do not have a significant effect on the faith, but customs that actually morph into faith are in themselves dangerous corruptions. Unfortunately, human memory is short so we do not have a clear idea as to when and where each custom developed.
To the contrary, we call ourselves 'ancient' and 'unchanging.' But the fact is we have changed -- anywhere from our Liturgy (5th century) to Palamite organization of the Church (13th century). We have gone through numerous heresies as well.
The Symbol of Faith calls Mary Theotokos. The words chosen are not accidental, because -- although the implication of motherhood is there -- the Fathers wisely realized that eternal God does not have a mother, but that the pristine vessel of Mary's womb served to Incarnate God as man. So, she was wisely named the "Bearer of God" -- and not the Mother of God, as the Latins translate.
I am curious as to who was the first to call her a saint and who and when was the first to say that she was assumed into heaven body and soul. Surely, the Epistles of the NT -- most if not all written after her death (some estimates are 48 AD) -- do not, and there seems to be no clear consensus of the Church on this issue at all for a few hundred years.
Don't get me wrong: I would like to be able to see that what the early Church professed and confessed was the same with regard to Mary as we do today, but our memories are short and simply because something is "ancient" in our eyes (don't you know -- grandparents were always old!) does not mean it was there from the beginning and was not invented or added as the memories faded and legends survived.
"I think that the most simple Russian or Greek peasant hearing the words of these hymns knew that Jesus is God and the Theotokos isn't, and interpreted the hymns in that light, just as we do today."
We peasants, or their children and grandchildren, still do! I, personally, even as a child, was never confused about this, and I doubt, Kosta, that you were either. :)