Your mistake is insisting that these issues of civil rights and environmental justice are separate from the dynamic of class inequality and wealth concentration. They are not.

While you can address the opportunity structure for some minorities through policies aimed at racial equality, you’ll never achieve for all unless you attack the class inequality at the root of racial privilege.

That is indeed the claim of the Sanders wing. It has been from the beginning of his efforts. That theory is a big reason why he lost in 2016, and why he lost in 2020. He believes that, but huge swatches of black voters don't necessarily share that view:

Democrats who wish to beat Trump but prefer Sanders to former Vice President Joe Biden, must ask themselves the following question: Can a campaign that rests primarily on class warfare and economic justice, one that largely relegates race to a concern simply encompassed by economic reform, attract enough black voters to prevail?

Recently, we conducted a national survey of the black community to answer this question. We found that if Democrats hope to mobilize the African American community, a Sanders-style message framing Trump as a threat to the poor and the working-class isn’t the best way to do it. If the goal is to maximize black turnout in 2020, a message emphasizing the threat that Trump poses to racial progress, according to our survey, is more effective.

politico.com - Why bernie sanders economic message isnt enough to win over black voters

As noted in that article, there's a big chunk of voters who don't believe that class inequality is at the root of racial privilege. They believe that racism is at the root of racial privilege. That you can't fix racism by going after the banks and oligarchs (to paraphrase Clinton's very effective attack on Sanders from 2016).

This is probably very frustrating to those who are historical materialists (like many socialists, and certainly Marxists), who have faced a lot of obstacles in raising voters' class consciousness and struggle with why the voters don't self-identify prioritizing class instead of other issues (or the way the voters used to act, according to the What's the Matter With Kansas). They believe the voters are wrong for not recognizing that class, not race, is what's most important. But whatever the reason, class consciousness has faltered in the face of other identity markers.

That's what I think is your mistake. I certainly don't believe that issues of civil rights and environmental justice are separate from the dynamic of class inequality and wealth concentration, but I don't believe that that the former are as strongly determined by the latter as I suspect you do (and certainly the Sanders wing of the party does). And I certainly don't think that the big chunks of the Democratic party that chose Clinton and Biden over Sanders in 2016 and 2020 believe that assertion, either. And I think the historical record supports their skepticism.