I agree with your main thesis that the word "liberal" doesn't mean what it once did.
I disagree with the comments on LBJ. There was nothing inevitable about the passage of Civil Rights bills in 1964-5. On paper there was no way to overcome Senate filibusters by Southern Democrats. Republicans might vote against cloture just as an act of partisan calculation. However, Johnson was a master politician and had an deep knowledge of the Senate and the Senators. He got the bills passed by forging an alliance of Republicans and Democrats, that reduced the die-hard segregationists to a minority that did not have the votes to stop cloture. He was one of the few leaders who could have gotten those bills passed. He would loathe the Progressive Democrats of today, not the least because of their disdain for the Senate and its institutions.