Do you accept that there are scriptures that indicate the deity of Christ? If you do, that would be the contradiction that believers were faced with. Jehovah of the OT with Jesus' claims in NT. The Jews rejected his claims, his followers accepted them. But there is the problem of reconciling the one God of the OT with Jesus and Holy Spirit in the NT.
But you already know that. And your conclusion is that it is polytheism. Fair enough!