The new Cadillac ATS coupe is the lovely, delightfully adept product of a Hobson’s choice. Luxury-coupe sales are stagnant, yet here comes a new luxury coupe because there are really no alternatives. At least the new ATS coupe is a hottie that’s gratifying to drive.

Here is the backstory: It’s so expensive to engineer a new platform that no company does it for just one mainstream model. After the high-volume sedan is developed, its guts usually get stuffed into another model as quickly and cheaply as possible. That leverages the component set with yet another new product that can reach a different customer, bringing in more sales at relatively little cost.

Thus, the BMW 3-series sedan, at which the four-door ATS is squarely [...]