I'm as cynical as anyone, doesn't mean there is no value in fighting to make things better though. Many of the gains from fighting for the right thing are at first unseen, and bear fruit later.
I hate to think of the things Hillary would accomplish with congress, the issues they could agree on are not ones I would want to see enacted, they would be the ones their donors want, IMO.
Did you watch the clip in the OP? Chris goes over examples re how Bernie actually knows how to work with opponents and get things done that still serve the interests of the people. His issues aren't driven by what his large corporate donors want, since he doesn't have any, and he manages to find ways to actually get amendments passed that help people (such as he got funding for community health clinics added the Obamacare as a condition of supporting the legislation).
Re your last paragraph, I think Bernie is just too polite to say that Obama used the grassroots to get elected, then abandoned them once in office, so instead Bernie says he would be different than Obama by staying connected to his mobilized electoral base to drive change. It will of course be difficult, in the first place to get Bernie elected, and in the second place to support him once elected. I doubt he has specific plans for that activism, but I don't doubt that he will use any tools at his disposal, one of the main ones of which is us, to push for change once he is in office.