Sorry but gotta disagree. While there is no American exotic marque that's equivalent to European brands like Lamborghini or Ferrari, there are models scattered about that compete with their European counterparts handily in raw track performance. I'd say the recently discontinued Dodge Viper and Ford GT Mk2 are the closest the US has to an exotic with the performance to match. As for models that compete with European performance like Porsche, you get the Camaro SS and ZL1 with the 1LE track package, Mustang GT350R, the Corvette C7 ZR1, and new Corvette C8. What makes American performance cars unique is that they forgo some luxuries for power, making them generally more financially attainable all while being competitive with their European rivals.
There are American luxury models as well like Buick, Cadillac, and Lincoln, but you are right as I don't think they're of comparable quality and refinement to Audi, BMW, and Benz nor are what most people think of when the word luxury comes up.