I’m afraid “the left” hasn’t had a clear meaning for many decades now.
The meaning of what is left and right shifts over time and whatever method you choose to place the middle is where biases appear.
If no party to the left of A has a chance of government and no party to the left of B has a chance of government, you’ve placed “middle” in the wrong place.
Ignoring political reality by starting a history lesson isn’t going to create changes.
It’s likely to lead to voters involuntarily disenfranchising themselves and not having any effect on the duopoly the system encourages.