BTW, we don't believe the Father and the Son are "separate individuals".
So if someone WERE to believe the Father and the Son ARE "separate individuals"...
Would their belief system be POLYTHEISTIC?
I say Yes.
Here is an overview of what I believe...
For this creation, YHWH God (the only one who transcends all creations) determined to create a universe with a kingdom of redeemed humans (living souls) for his glory where he would reign as a living soul himself. The Scriptures describe how God would accomplish his plan. In an instant, transcendent God (called God the Father) created the supernatural and space-time of this universe and also became immanent as a spirit (called the Spirit of God) and in the form of a living soul (called the Word of God) with a glorious body. God the Father then created all things within the universe by the power of the Spirit of God commanded by the Word of God. But whereas God created a human spirit and soul for each of us, God himself as the Word became the human spirit and soul of Jesus. At his conception, Jesus' glorious body was changed to a mortal body to be made like us so he could make reconciliation for our sins. At his resurrection, Jesus' mortal body was changed back to a glorious body and he will also give each of his elect a glorious body when he returns to reign in his kingdom forever.