Which text did you have in mind that mentions multiple demiurges? (I can't think of a one I've read that does.)

The important thing to ask about historical rejections is "why?"

Gnosticism bears the marks of disappointment: I can't imagine a non-Jew in Antiquity being that interested in the book of Genesis or exactly in what was wrong with the Jewish deity and the traditional account of his words and deeds. The way Gnosticism thinks also looks more Jewish (remembering to include all the Jewish literature since the rebuilding of the Temple) than not; the peppering of Aramaic names and puns in Gnostic literature adds to this impression.

-Kushana Torumekia