It's quite the opposite of remarkable - Clinton was not only the clear front-runner, she was ahead in all polls by a sizable margin (that Sanders caught up as much as he did is a credit to him).
Frame it as "DNC positions themselves as an ally of the predicted nominee given no strong challengers at that time" and it sounds pretty... normal.
Did any of the documents release suggest that they were helping HRC _against Sanders_? Or just that they did work that would help her against a GOP candidate?
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.
Are there leaked documents that contradict this statement? When they're not administering primaries, the DNC spends most of their resources trying to get nominees elected in general elections. Of course they've been working on strategy for Clinton.
Frame it as "DNC positions themselves as an ally of the predicted nominee given no strong challengers at that time" and it sounds pretty... normal.