While I think that most of your descriptions of progressive ideals and motivations are wrong (stubborn "purity test" politics, broad irresponsible economic outlook) I am not willing to die on the hill of party identity. It may be wiser for certain people to take their views on corporate influence, build a separate party around that and quit doing things like challenging Dems in primaries. That could only work under one condition though. As a parting gift, Democrats would have to promise to make the elimination of FPTP voting a state by state priority so we can coexist in relative peace and acheive third party feasibility.

Another option is to stay the course of slowly leaning left while waiting out the generational shift, as you suggested. Personally, my support for left wing politics is predicated almost entirely on a sense of urgency regarding an impending environmental and societal collapse. Otherwise I'm a fairly conservative guy. This option admittedly challenges my worldview. There's also the chance that if we wait, will the party leadership will just ice us out and ultimately shift right again, which has been the macro trend.

Then there's the implied option: "Progressives" grow up and learn to work as a team against a common enemy and return the party to sanity and drop the purity tests and yada yada. Unfortunately, there is plenty of evidence to suggest that mainstream Democrats are unwilling to fight