The author of that WSJ piece is Epstein himself, who also authored the book under review. Your statement at the end basically says, we have classified sources

The author of that WSJ piece is Epstein himself, who also authored the book under review. Your statement at the end basically says, we have classified sources saying Snowden was a Russian/Chinese spy, and we have "feel-gooders" like Oliver Stone saying otherwise, so who do we trust? The submitted article is by a reporter more neutral and level-headed than either Epstein or Stone, and he basically concludes: there is nothing at present but wild conjecture supporting the "Snowden was a spy" theory. So I think that may be the answer to your implicit question.