On the other hand, what some of those on the left of the Democratic Party are now thinking is that the reason they wield very little power is because they haven't credibly threatened to destroy the Democratic Party. Those further to the right (see: Joe Manchin openly talking about maybe switching parties; see also, Jeff Van Drew actually switching parties) wield power because the Democratic Party would be devastated if they switched to the Republican Party.
So what at least some on the left are now saying is, if we don't credibly threaten to sink the Democratic Party in this election by sitting it out--and follow through if necessary--we won't be taken seriously going forward.
I agree that Congress is at least as important (but then, Bush, Obama and Trump have all pushed the "unitary executive" theory where the executive gets to do whatever it wants unless Congress explicitly says no, and even then the President can veto it anyway) but the Presidency is the flashpoint race. It gets the attention, it drives turnout for downballot races.
I disagree with this, to be clear; Justice Ginsburg's age would be enough to make me go vote for Biden were I eligible (as it is, I'm just an outside observer who is nonetheless significantly affected by US policy). But I can understand where others are coming from on the point.