What's your alternative?
Do you have a ready-built national organization that can be successfully co-opted to supplant the DNC i dont know about?
DNC isnt just a sunk cost, its an established civic investment. Unless you think the whole system is going to collapse overnight, a takeover of an existing party is the quickest way to get real change. And if the DNC is rotten and needs to go, we can best do that from the inside.
Every "third party" either merges into a major party or devolves into a vanity party, because the only positions that matter electorally in a winner-take-all system are "i suooort the current person" or "i want them out of office."
Ignoring Bernie for the moment, "against the working class" is usually a dogwhistle for "poor whites have racial nervousness and i want to exacerbate that for political gain.". You wont find real examples because, generally, professional democrats arent against anyone. (even nazis, apparently.)
Bernie's specific crtique was a slightly tone-deaf critique that the dems were largely silent on the economic nervousness of the working class, and instead spend political capital fighting for racial and gender equality. Since the white male working class is not oppressed by race or gender, or in a position to really oppress anyone, they often feel unrepresented.