I'd like to agree with you but in America I think a portion of lefties have this utopian third party rising hope. Historically it just doesn't happen because the electoral college and state ballot requirements throws a wrench into the formation of a strong third party.
A democracy such as France with coalition party politics can result in a third party emerging out of a cloud suddenly as it did in their last election. But their new party is a centrist one and who knows what will be the long term conditions as so many of their candidates have zero political experience. Their democracy is now ladled with rookies. Some say that is a good thing, but contrasting, experience counts.
At any rate, where's that lefty third party to supplant the Democrats? The Greens? There's a party shooting itself in the foot. Jill Stein was not well known and had no political experience (actually working as an elected official). Then she went on some sort of Clinton helping crusade (publicity stunt?) after the election was over.
It's depressing to me. I'm disappointed with the Dems but where do I go? As it stands today, it appears that trying to change the party from within seems the 'easier' path, thus the Democratic Divide now raging. The Progressive Wing needs to win that battle.