And for all we know there are also documents prepared in support of Bernie Sanders which, if leaked, would paint the parallel picture of DNC supporting him.

And that's assuming these documents are complete and unmodified. Nothing stopped this hacker from selectively editing and selectively leaking to support their agenda.

It seems relatively obvious that the DNC would have had teams preparing for both scenarios. The only difference is that Sanders has been a viable candidate for a shorter period of time.