I agree with you that Dems are better for the economy across all economic levels of Americans.
I think Dems have got to do a better job discussing economic issues. Dems tend to get a bit caught up in showing how the economy is better using facts and figures and economic data...and most voters essentially equate "the economy" with their personal budget. Dems have got to find an economic populist message that works with those who aren't white collar professionals in reasonably high paying jobs. It's going to take hard work because Dems have to thread a needle of being realistic with what can be accomplished while also setting a vision that is beyond the strict reality of where we currently reside.
I think motifs of economic mobility, ensuring an opportunity of a "good life" for all, fighting corporate greed, and similar ideas will be the foundation of that message. But it will not be easy to really determine and will take a lot of effrort.