The child that Mary conceived and bore was not the Father. The child that Mary conceived and bore was not the Holy Spirit. So, no, Mary is not the mother of the Triune Godhead. But Matthew and Luke both tell us that she conceived and gave birth to the Son of God.
And yet saying *mother of GOD* says exactly what you are denying, while using the term the Holy Spirit used in Scripture, *mother of Jesus* DOES say what you are stating.
When you say *God* to people, who or what do you expect them to think of first?
And if you are meaning *Jesus* in a conversation, don't you specify that it's Jesus so as not to be confused with the Holy Spirit or the Father?
Catholics can try to explain away, excuse, justify, and rationalize all they want how *mother of God* is the same as *mother of Jesus* but is simply is not the case.
They say two different things.
Colossians 2:9 For in him dwelleth all the fulness of the Godhead bodily.
Seems he's got a problem with that comment.
The angel Gabriel told Mary that the holy Child that she would conceive in her womb, give birth to, and name Jesus, was the Son of God. Given that the Son of God is God, this makes Mary the mother of God.