In many ways for many people, things have gotten better. Over a 60 year period. Things are better from the perspective of social issues but not in terms of prosperity.
Can't argue that recent history is as you say. I simply can't get behind the idea that Democrats were not progressive or left leaning enough. Democrats will have to peel a few states from the GOP to win back the White House or Congress. You say that going more progressive would accomplish this. I don't understand this way of thinking. I don't see evidence that it is true.
On the other hand, I think the average voter is fed up with campaign funding corruption. Bernie was right to make it a centerpiece of his campaign. The GOP is on the wrong side of this argument and it is one issue that Democrats own outright. But it is not as important as bread and butter issues like wage stagnation and jobs. This is the area where Trump, if not the GOP won in 2016. There is no reason why Democrats should have been beaten in this area except for their own negligence.