Christians: Question Regarding One GOD vs. Trinity / Triune God?

The trinitarian God is one. Christianity is monotheism. While the church has always taught that essentially at the heart of it Trinity is mystery, the objection raised by "non-trinitarian Christians" (a misnomer if ever there was one) that because the finite creature man is bound to one person in one being, that God too must be bound to one person in one being is clearly anthropomorphism.