I'm not sure why you find it reductionist or presumptuous. It's not my interpretation, it's an alternative Christian theology that goes back way, way back. Moreover, Gnostic beliefs are not merely a differing interpretation of the Bible. There are quite a large number of gnostic texts that differ significantly from the official Biblical canon.

I don't think Gnostic Christianity is responsible for anti-semitism either. I concede the argument about the OT God = evil and NT God = good, except that mainstream Christianity, and most of the Christian anti-semites I know, hold the God of the Old Testament to be the same God of the New, and reject the notion that they are separate deities. The Christianity of today that we inherited from the early Church bears very little resemblance to gnostic Christianity, enough so that I don't think gnostic beliefs can be held responsible for antisemitism.