But we don’t “name” them three, as if giving vaule by the name we give them in some sort of nominalistic fashion, rather we recognise the reality of God being three persons in one substance and one substance in three persons. To say that God is three persons is to exclude the possibility of God being 2,4,5,6,7 etc. persons. To say God is three persons is to make a definative statment about reality.
"The Trinity is One. We do not confess three Gods, but one God in three persons, the ‘consubstantial Trinity’. [Council of Constantinople II (A.D 553)]
Note this is not at least three persons, but three persons; the Trinity. Again to name something definitively as Trinity is to exclude the possibility of it being a quaternity or anything else.