You make some good points, though it’s a little more complex. For instance, many counties in the rust belt flipped from Obama to Trump—which shows that more than racism and cultural issues were at play. And Bernie Sanders handily won Michigan and Wisconsin in the primary—it’s likely he would have held on to them in the general.
What turned off many rust belt voters about Hillary was her perceived pro-free trade positions—her past support for TPP, and her husband’s passing of NAFTA (it may be sexist, but many associate Hillary with Bill).
Going forward the best path would be a balance between holding down the current ‘Obama coalition’ while still reaching out to the working class (note I said ‘working class’, not ‘white working class’). Economic populism is key—it’s time for Democrats to support labor, and emphasize the bread and butter issues that effect the majority of Americans (i.e. jobs, education, wages, etc.).