Respectfully, I see and agree with what you say, except I think he sees the left as being much more uniform, monolithic and cohesive than it currently is, and sees much more difference between the parties, as regards the tension between principle and practicality, than exists (or probably can exist outside of cases like the communists).
I see where you’re going. The Democratic party has been pulled to the far left and that is their control center. Certainly they don’t all agree, but you will not see much of this division played out on the national stage (media will focus on making us the devils and their party the angels for the benefit of vote getting).
Perception is a very, very powerful tool.