Joseph (in Joseph and Aseneth) is called hO hUIOS
TOU QEOU (6.2). God also refers to the King of Israel as "my
Son" in the OT (Ps. 2:1-12). Yet I will agree that Jesus is
uniquely God's Son (John 1:18; 3:16). Nevertheless, you have not
presented any lexical evidence to support the
assertion that the noun phrase "son of God" takes on
the meaning "possessing the nature of" or "possesses
every objective property of" God when the term is
applied to Christ.
Addendum: Adam is also identified as the son of God in Luke 3:38; Compare Job 1, 2 & 38 where angels are identified as "sons of the true God" or sons of God.