Assange has a history of promoting himself. He went on and on about how he had much more from Bradley Manning, and when it was finally released it was mostly boring stuff.
On the other hand, we really don't know for sure who hacked the DNC servers. Might be the a Russians. The Russians, same as us, are very good at hacking into computer systems. If anyone really believes that Clinton's unsecured private State Department email server wasn't hacked by the Russians and everyone else who wanted to get in there, they're fooling themselves. Gmail servers have more security than hers did. In any case, you can bet the NSA has all of those deleted emails.
But the bigger bombshell for Clinton may be her own ties to Russia.
The Clinton Foundation, State and Kremlin Connections