literally millions of times over.
As for your concerns about unity, the good news is that by far most groups and individuals in our very diverse coalition are united to achieve common goals. Don't worry that not all are; we're Democrats, not ants.
But just look at our candidates: a large majority, including all those who are believed possibilities to win, are from the large, diverse coalition and running on remarkably similar values and goals. And look at the midterms: almost all of the many new Democrats elected are part of our large, united majority.
Prog2020, we seem to agree that achieving goals requires creating working majorities. Being progressive also requires committing to and doing what is required to make progress happen. Otherwise, it's just posturing, a label, a banner to fight under.
You should ask yourself what the real goals would be of a subfaction that would insist everyone who doesn't belong to their group is not progressive. (The current rejecting term in your post is "centrist," completely ignoring where people actually are on the L-R ideological spectrum.)
Actually the main working difference has nothing to do with our common progressivism. Rather, we have a large progressive group made up of millions of individuals and many cooperating factions and a smaller, more zealous one that must oppose the larger group because it is the larger group.
(Denial-spoiler alert: This has been studied many times over.)
Now me, I am a lifelong strong liberal, so naturally inclined to acceptance of and cooperation with others of various opinions, especially when they constitute a power center that can succeed. And of course as a liberal Democrat I believe strongly in progressive government. Therefore, I am inevitably part of the larger coalition united to achieve common goals.
As for the word "centrist," our grand coalition ranges from strongly left wing to, yes, centrist and/or blue dog, though centrism is out of fashion these days and there aren't many. That's unfortunate, btw, because America needs a strong coming together at the political center to survive. America must eliminate that giant divide-and-conquer rift.
Hope this picture helps, and that you will consider where your place in it should be. There's of course no end of good work to be done.