I respectfully disagree with your analysis of the EO position on original sin. I have read statements by EOs that the problem they have with Augustinian formulations is with the transmission of original sin, not the fact of original sin.
And I respectfully disagree with you. Eastern Orthodoxy doesn't even call the first sin "the original sin" but "the ancestral sin." Furthermore, since EO doesn't make distinctions between nature and grace and thus rejects the notion that grace is antecedent to man's responst to G-d, it could be understood as a Pelagian, or at least Semi-Pelagian, religion.