You seem to be confused about what this thread was discussing. The question was whether Assange received the emails from an insider or a third party. Who actually did the phising is a separate concern.

That said, considering the context of the election, Trumps close ties with Russia and Russian agents, and the broad and multifaceted attempts at hacking the election attributed to Russia (disinformation farms, hacking state election networks), it is very likely that Russia was also behind the DNC hack. These weak attempts at casting doubt on Russia's involvement are transparent.