When thinking about ANY father and his son, is it commonly regarded as them being co-equal and the same person? Of course not.
So if God and Jesus both always existed and are co-equal, then why would the Bible confusingly speak of God and Jesus in terms of a relationship between a father and his son?
If God and Jesus really are equal, then it would make no sense for the Bible to phrase them as "Father" and "Son".
The word "son" principally is regarded in the Bible as "offspring" and in Genesis we read that Adam was produced by God. Interestingly, Adam and Jesus even shared the same description: "son of God". (Luke 3:38)
While the Father is always found in the Bible to be called "God", the phrase "God the Son" is never found. Further, if the Son really was God, then why would he call the Father "the only true God"? (John 17:1-3)
Jesus is God's "only-begotten" son...the only being directly created by God. (John 1:18) Therefore the designations "Father" and "Son" make sense and are appropriate.
For more, see
Only-begotten god (OBGOD)