I upvoted you, because that's a great point on financial solvency.
However, it doesn't address the long-run problem of how to take back market share from foreign competitors, which is the type of sustainable advantage that I presume Detroit needs in order to thrive.
(I'll also observe that your QED was to a simple P&L equation, not to the thrust of my comment.)
They have strong market share. GM is still #1 here and in the world overall (though just barely). Market share isn't their problem, it's that they have to sell at a loss to maintain it.
The reason Toyota has all but caught up isn't that they're particularly innovative, it's that the Camry can have $2,000 worth of better build quality than the Taurus or Malibu. Same with Corolla vs. Focus.
Japan gets to choose to either build the same cars and sell them cheaper, or build better cars and sell them for the same price. It's hard to win market share in that scenario.
In 2005 GM sold about 4.5m cars in the US. At $2k per car, that's $9 billion in extra revenue. That flips them from a $4b loss to a $5b profit.
QED.