Are you disputing that fact that they then declared Mary to indeed be “the mother of God”? Surely you understand what the dispute with Nestorian was. Trying to hide that fact that the declaration was part of the result of that dispute seems evident an attempt to hide that fact that Mary was declared the “mother of God” and “queen of heaven” in the same city and society that already understood the queen of heaven concept having worshiped Diana the queen of heaven. Can you say adapting pagan understanding and practices to entice locals to Christianity?
You are faced with a predicament that most of Protestantism has rejected from which you must choose the teachings of the Catholic Church or the path of heresy.
The Counsil of Ephesus was called to address the Nestorianism and to affirm the Nicene Creed as the cornerstone of Catholic Christianity. They declared the nature of Jesus to be both and simultaneously 100% man and 100% God. That Mary is the Mother of God was not a declaration but a logical conclusion. You would do well to read the The Twelve Anathemas of St. Cyril Against Nestorius (and apparently you).
1 If anyone will not confess that the Emmanuel is very God, and that therefore the Holy Virgin is the Mother of God (Θεοτόκος), inasmuch as in the flesh she bore the Word of God made flesh [as it is written, The Word was made flesh] let him be anathema.
2 If anyone shall not confess that the Word of God the Father is united hypostatically to flesh, and that with that flesh of his own, he is one only Christ both God and man at the same time: let him be anathema.
3 If anyone shall after the [hypostatic] union divide the hypostases in the one Christ, joining them by that connection alone, which happens according to worthiness, or even authority and power, and not rather by a coming together (συνόδῳ), which is made by natural union (ἕνωσιν φυσικὴν): let him be anathema.
4 If anyone shall divide between two persons or subsistences those expressions (φωνάς) which are contained in the Evangelical and Apostolical writings, or which have been said concerning Christ by the Saints, or by himself, and shall apply some to him as to a man separate from the Word of God, and shall apply others to the only Word of God the Father, on the ground that they are fit to be applied to God: let him be anathema.
5 If anyone shall dare to say that the Christ is a Theophorus [that is, God-bearing] man and not rather that he is very God, as an only Son through nature, because the Word was made flesh, and has a share in flesh and blood as we do: let him be anathema.
6 If anyone shall dare say that the Word of God the Father is the God of Christ or the Lord of Christ, and shall not rather confess him as at the same time both God and Man, since according to the Scriptures, The Word was made flesh: let him be anathema.
7 If anyone shall say that Jesus as man is only energized by the Word of God, and that the glory of the Only-begotten is attributed to him as something not properly his: let him be anathema.
8 If anyone shall dare to say that the assumed man (ἀναληφθέντα) ought to be worshipped together with God the Word, and glorified together with him, and recognised together with him as God, and yet as two different things, the one with the other (for this Together with is added [i.e., by the Nestorians] to convey this meaning); and shall not rather with one adoration worship the Emmanuel and pay to him one glorification, as [it is written] The Word was made flesh: let him be anathema.
9 If any man shall say that the one Lord Jesus Christ was glorified by the Holy Ghost, so that he used through him a power not his own and from him received power against unclean spirits and power to work miracles before men and shall not rather confess that it was his own Spirit through which he worked these divine signs; let him be anathema.
10 Whosoever shall say that it is not the divine Word himself, when he was made flesh and had become man as we are, but another than he, a man born of a woman, yet different from him (ἰδικῶς ἄνθρωπον), who has become our Great High Priest and Apostle; or if any man shall say that he offered himself in sacrifice for himself and not rather for us, whereas, being without sin, he had no need of offering or sacrifice: let him be anathema.
11 Whosoever shall not confess that the flesh of the Lord gives life and that it pertains to the Word of God the Father as his very own, but shall pretend that it belongs to another person who is united to him [i.e., the Word] only according to honour, and who has served as a dwelling for the divinity; and shall not rather confess, as we say, that that flesh gives life because it is that of the Word who gives life to all: let him be anathema.
12 Whosoever shall not recognize that the Word of God suffered in the flesh, that he was crucified in the flesh, and that likewise in that same flesh he tasted death and that he has become the first-begotten of the dead, for, as he is God, he is the life and it is he that gives life: let him be anathema.