Yes, I think we're in agreement.
On your final point, I'm more optimistic. For Sanders personally, it's too late. He's too old to run again, so he doesn't get to sit in the big chair. But the future for left-wing politics in America is maybe a little rosier than you assume. I'm not at all a fan of splitting people into 'generations', as I don't actually really believe they exist. However, it is true that the composition of the Democratic electorate is shifting to the left, and that the cause of this shift is increasing left-wing ('liberal' or 'socialist', rather than 'moderate') viewpoints among younger voters. This goes together with a shift to the left in the congressional Democratic caucus, which has gone largely unremarked because it pales in comparison to the leap to the right on the other side, but nevertheless is clearly happening. Finally, I think the macroeconomic situation favours broadly left-wing politics over the long run, from secular stagnation to the global investment dearth and the increasing competition for hours.