Gnostic Christians believe two Gods exist; an evil God who is the God of the material world as described in the OT and the good God who is the God of the spiritual world as described in the NT. That's two Gods. That's polytheism.Yu are just putting words in my mouth.
Polytheism is worshipping more than one God.
Gnostics only worship one God. The true God.
But acknowledges that God is not alone. There is a system in heaven of numerous entities. The Christian Bible says the exact same thing, just doesn't spell it out like Gnostic writings do.
On face value Gnostic Christianity starts from an indefensible position. There are no texts which exist that even make the claim that there are two Gods.