Not saying primary support is necessarily indicative of general performance in any way, but the GOP outvoting the dems in blue MI should be at least some cause for concern among democrats.
A reasonable analysis and part of me wants to be encouraged by what you say.
But since the MI primary, I've been bothered by that massive polling miss on the D side. That was an out of this universe polling error.
My gut says there was a significant component of D crossover "meddling" voting for Trump. (Remember, Michigan was an open primary.) This could explain the D-side miss, however, the R-side relative accuracy doesn't back that up. So I know it's a very debatable theory.
My point being, I'm not hanging my hat on the big R primary turnout. Even without crossover/meddling effect, it's arguable D primary turnout was suppressed by the expectations that it wasn't at all competitive.
All of this is quite possible. We'll just have to wait and see.
One caveat - MI has a relatively high black population as compared to other northern sates (Trump's biggest obstacle there). However, if black turnout is falling 10-15% lower than 2012 (as it is in many swing states) Hillary may be in trouble. Because dems win blacks by 9-1 margins, even a marginal drop-off could have a large effect.
We will see.