I think you are correct in that the design culture has moved from the US to Europe, as it seems it is Ford's European designers, not its American designers, who are on the cutting edge.
Wasn't Ford also planning on releasing a new Mustang model that was based on a European platform?
Bottom line: While the US auto-industry continued to decline, they still did well enough with "light trucks" to survive. That is pickups and SUVs. Big vehicles, big V8 engines. Nothing particularly innovative there.
Meanwhile the international competition was advancing towards the next era, evidenced by the investment Toyota made in hybrid technology. And the investment VW Group made in clean diesel technology.
The problem for US companies is this: the competitors are not standing still. Once behind, the US firms stand little to no chance of leapfrogging to the front.
The Europeans use racing, to advance and to showcase technology. Audi (VW Group) have dominated LeMans racing, using diesel technology. Formula 1 uses variations of hybrid bits.
Meanwhile Nascar goes around and around ovals, in low tech vehicles, to the delight of their undemanding fans.
With a few exceptions, US firms simply don't participate in the highest levels of international racing.