The left is not relative, nor has the meaning shifted in all this time.
The left is the same communists and anarchists it has been for over a hundred years world wide now.
Political party popularity does not change political ideological meaning.
And the American system doesn’t encourage duopoly, it literally enforces it. So yes, of course many leftists are going to feel disenfranchised after close to a century of being villainised and neglected by their “representatives”. The solution to that is for a party to adopt leftist ideals, but that goes against the interests of the ruling class who’s money and influence runs the game.