I think you're missing the financing costs involved in moving product.
While Korean autos will ship by sea, it often makes economic sense to ship lighter, higher value per unit weight products by air, even if fuel costs are high.
Air freight was hurt more by the global recession than by the cost of fuel.
Very old and thirsty aircraft may now be economically obsolete, even as freighters, but there will be plenty of later, more efficient ex-pax aircraft coming to market for conversion as time goes on.
As others have pointed out, fuel costs are but one part of the equation.