No, the argument that I gave in 329 is sound (i.e. the premises are true, and the conclusion follows necessarily from the premises), whether or not Mary gave birth to a male child.
-A8
"The original point that you were trying to make (in 283) was to show that Mary undergoing the purification rite shows that Mary was impure"
"the premises are true, and the conclusion follows necessarily from the premises"
No, your original statement is false, therefore your conclusion is false. My original point was that because Mary gave birth to a male child she fits within the requirements of the Law that says she is impure and must go through the purification rites.
Jesus was sinless and did not need baptism to purify Him from sin, He submitted to it voluntarily to identify with sinners and to confirm to John He was the Messiah, the Son of God. For Jesus, baptism was necessary to fulfill the Law as a sign; for Mary, purification was necessary to fulfill the Law because she was impure.