Sadly, things are not that simple. Internationally though, things are very different.
Selling Jag? it sells well internationally, outsells Lincoln easily. So what lincoln does well in the US, nobody cares about it in most other parts of the world.
Land Rover? nope, same thing as jag. Aston Martin isn't great, but at the same time, it's still showing a much smaller negative number than Ford itself. Also, Ford is loosing money in the US market, but it does well in other parts of the world as well. I am in no place to say what ford should do, but it's certain that the problem has nothing to do with their brands, but the stuff they are chugging out.
Same thing pretty much for GM. Corvette aside, Chevy and GMC has been known for their trucks. In a few years when gas is 6 dollars a gallon, these two brands will naturally go down. Focusing on these two brands is suicide. Get rid of pontiac? Sporty Saturn?
things just isn't as simple as most people thought.