They aren't winning elections at a high enough clip to inact the changes that make progressive base happy.
My personal opinion is that they have helped move to overton window to a place where positive policy discussion and implementation is happening.
They just aren't going to overthrow the Democratic party.
They've certainly failed at rapping into the apathetic voter base they though would propel them to prominence.
That's pretty fair. I'd say shifting the overton window and creating a better space for more leftist politicians to succeed was more or less the short-term goal for a lot of us. The overthrow people always got magnified because they make for better media and were valuable to attack (ie: Bernie Bros); but they're more representative of a section of the support rather than the broad majority.
The folks who expected this to be a Tea Party level of success do represent a significant chunk, but not a majority. They've also split on Bernie and the Squad. A decent amount of even these heads will go lesser-of-two-evils when it comes down to it. That applied even to Biden.
The attempt to create a new voter base does seem like it's fallen well short of what most of us hoped for. At the same time, I don't think the rest of the voter base is impossible to flip as this messaging and their policy prescriptions become more familiar. Where progressives have succeeded, they're electoral success has grown not shrunken. I think that speaks to their actual constituents' feelings (rather than media personalities and national sentiments toward them) and there's opportunity to improve the appeal of these politicians over a longer span (if I'm not mistaken, Turner did markedly better than Bernie's primary numbers vs Biden for an immediate example. Cori Bush needed a second try. I'm watching Cisneros in '22 to see if she can keep that trend too).
I think the pragmatic view has always been to understand the limitations of electoral politics short term and to understand that activism is still going to play a big role in short-term victories. That's something that I think Bernie was fairly explicit about, but that was misread by some people (some in good faith and some in bad faith).