Meanwhile, thus far the "farther-left (and maybe even insurgent) Democratic wing" for all the noise it seems to make has had little effect on the party. They aren't electing people, they aren't even really challenging incumbents very much.
Contrast this to the steady rightward march of the Republicans over the last 30 years: the rise of the Evangelicals in the 70s, Gingrich's 1994 "Republican Revolution", and more recently the Tea Party wave of 2010 and the explosion of an apparent Trump faction. All of these lead to not only actual electoral victories, if not dominance in the Republican Party in some cases, for the more extreme factions, but were coupled with real threats of incumbents who didn't play ball being "primaried" by more extreme challengers.
As I said, it's possible that the surprising performance of Sanders and the popularity of people like Warren may be the beginning of similar change in the Democratic Party, but until that actually happens it's just not comparable to what's happened to the Republicans.