I'm going to vote for the democrat this November but I think most folks who talk about this issue are not disingenuous. Voting in the presidential election is a bare minimum, minimally effective political action. For me and most of the people I know it matters almost not at all because I don't live in a swing state. My local elections matter a hell of a lot more.
There are limits to the effectiveness of electoralism that are worth understanding. I think a lot of folks who talk about the Democrat's failures are advocating for political action beyond voting. Direct action is a far more effective form of political action that people should be putting their energies into.
Union organizing, renter's orgs, housing activism, talking to your neighbors, local politics, and lots more are much more effective ways to assert power in your life. Voting makes me feel helpless. We need to act as well. The primary thing preventing positive political change is the belief that we can't do anything to bring that change about.