That's very simplistic and not very credible. What part do you disagree with and why?
I asked if a teenaged girl betrothed to a man who just gave birth to a child not fathered by the man to whom she was betrothed would have authority in first century Jewish culture to name that child the "first born" of the family, even though He was not the offspring of her husband to be. You did not answer, though you really want the title Mary's "first born" as applied to Jesus to mean the standing of the honored child in the family, not the first of multiple children born to her. Let's start with that one. Who gave Jesus the title of Mary's Firstborn?
Scripture makes it clear Jesus is God's ONLY son, yet Mary's FIRSTBORN. You tried to make the point that He was designated as such so as to be the "honored" child, the inheritor with the birthright. I simply asked how that could be, as there is no record of Joseph naming Him that, especially if, as some are claiming, Joseph was an older man who already had children from a previous marriage and therefore would already have a child with the birthright. He would have been insulted in that culture as illegitimate, not honored.