A lovely ideal, that. But utterly pure Platonic function-shaped forms are hard to come by. Setting aside the exquisite chicken egg, I really can't think of a single example of architecture or industrial design that is universally acclaimed to be perfect.
In part, that's because objects used by people usually have more than one function to fulfill. For instance, a knife has to have a blade that will cut. But different kinds of things are best cut by different kinds of blades. And knives must have handles, and those might vary in shape and material. So there is no real-world Platonic knife.
Automobiles, as I've pointed out more than once, have the function of being sold, something that at times can be at odds with design purity. Setting aside the current needs for aerodynamic efficiency and compliance with government safety regulations that affect appearance, one might consider functionality in terms of the visual expression of a car's major visible engineering components and how well the forms express these.
As it happened, such conditions and expressions began to disappear when cars designed by styling staffs began to dominate the American market in the early 1930s.
Let's take a look at a typical American car design at the point when they were about to be succeeded by professionally-styled models. In this case, the 1929 Chevrolet AC.