No, it is not formulaic language if by that you mean a code word with a meaning artificially attached, like when we say "nine one one" and mean "emergency". Mother is one giving birth. Jesus Christ is God. Mary gave birth to Jesus Christ. She is mother of Jesus Christ. She is mother of God.
You mentally insert preexistence into motherhood. It is not necessarily true even with my mother, or yours, because we don't really know when my soul or yours began to exist (we know that our ensoulment predated our mothers' ensoulment, a different thing). It is surely not true with the conception and birth of Christ, because the scripture tell us so. When we ask, -- How? the scripture answers, -- Because all things are possible with God. Mary is the mother of God Who preexisted her in the most direct unconvoluted straighforward sense.
Your response confirmed what I wrote.
You do not think that Mary before the God came into being. (Which is a good thing, since God is eternal.)
I sense Nestorian thoughtwaves in thems that don't like calling Mary the "Mother of God."