"I think the great divide between religious peoples is between those who believe that the creation is the central story, and the point of it is that creation is good, versus those who see the fall as the central story. Is humanity essentially good? Or is humanity essentially depraved?"
While this is certainly bad theology (he brushes off The Fall and its implications), I don't think it can be considered Gnostic as he at least understands that the Creation was Good.
I think we may be going in circles. Of course there is more than gnosticism in the mix of heresies at the heart of ECUSA. But gnostic thought is one of them at the very root. The specific idea that "love" and "spirit" can be utterly distinguished from biological bodies is a gnostic idea. That such a distinction may be used as a rationalization for sexual liscenciousness is a gnostic application of that distinction. This is clear.
Does this make Gene Robinson et al textbook 2nd century Greek gnostics? No. As you point out. They have abandonded the utter anti-material philosophy of the early gnostics. Does this mean that the argument they make for seperating sex from spirit is less gnostic, no. It is an exact reproduction of a gnostic line of thought based on the very same gnostic principles. soul v. body, flesh v. spirit etc...