This is correct, but it's worth noting that voting is a bare minimum level of engagement. Despite the rhetoric from the establishment, exit polls show that progressives have been remarkably consistent in showing up to vote for shitty establishment candidates. What they won't do is donate to their campaigns, or volunteer their time, effort, and expertise. Nobody wants to knock on doors for a candidate they can barely stomach voting for.

There will always be an enthusiasm vacuum for establishment candidates, and that matters. That is a big part of why the DNC is already $2million in debt going into this election, despite the expectation of a blue wave.