As such, it is acceptable as a doctrinal statement because it provides an exposition of scripture that is coherent with and supported by scripture.
That is a circular argument. That’s like saying the Bible is God’s written Word because it is God’s written Word. Your Confessions provide doctrines that are not in Scripture (sola sciptura) or are contradicted by Scripture (sola fide cf. James 2:24). The Lutheran traditions of interpreting Scripture and putting those interpretations into a Book of Concord, are just that, traditions of 16th-century men without Apostolic Succession and/or authority that use the authority of Scripture as a pretext to guise their false interpretations of Scripture. Our Lord founded the Catholic Church, Lutheran founded his own ecclesial community. Facts are facts.
Assumption of Mary that finds no scriptural basis and is actually first supported in writings declared to be heretical by previous Church councils that recognized their gnostic influence and origin
That is a claim. You provided no evidence. You keep touting these claims without substantiating. Do you think we are foolish? Even your community’s founder believed in the Assumption of Mary, along with the Immaculate Conception and her perpetual virginity. Take notes: I just claimed something, now I will substantiate it with historical facts.
“It is a sweet and pious belief that the infusion of Mary’s soul was effected without original sin; so that in the very infusion of her soul she was also purified from original sin and adorned with God’s gifts, receiving a pure soul infused by God; thus from the first moment she began to live she was free from all sin” (Sermon: “On the Day of the Conception of the Mother of God,” 1527).
“She is full of grace, proclaimed to be entirely without sin—something exceedingly great. For God’s grace fills her with everything good and makes her devoid of all evil.” (Personal {“Little”} Prayer Book, 1522)
In his sermon of August 15, 1522, the last time he preached on the Feast of the Assumption, he stated:
“There can he no doubt that the Virgin Mary is in heaven. How it happened we do not know. And since the Holy Spirit has told us nothing about it, we can make of it no article of faith… It is enough to know that she lives in Christ.”
“It is an article of faith that Mary is Mother of the Lord and still a virgin. … Christ, we believe, came forth from a womb left perfectly intact.” (Weimer’s
The Works of Luther , English translation by Pelikan, Concordia, St. Louis, v. 11, pp. 319-320; v. 6. p. 510.)