A more exact objection asks what union means if God is treated as a transcendent spiritual reality while Jesus is understood as an embodied human being. Does “union” merely denote a special relation, or the becoming of two realities into one being?
The ordinary relationship of soul and body is a feature of human life, but an analogy from that relationship cannot simply be projected onto the divine essence. Proximity, influence or mediation alone does not prove identity of substance.
The disputed analogy crosses distinct categories: an unlimited Creator and a limited embodied human are not automatically related as the constituents of an ordinary human being. A conclusion of ontological union would require evidence beyond the analogy.