How do you know the ancient Gnostics weren't right about Jehovah?

The Gnostics believed that Jehovah was dipicted as a wrathful and jealous god in the OT because he is an evil god. Their cosmology says that Jehovah was once a son of the goddess Pistis Sophia, but he wanted to seperate himself the oneness and unity of all the gods, so that he could stand alone and be the only god. He tainted his creation with his jealousy and malice. What do you make of this?