Analogously, we can see that nearly all of the optimization power of human engineering must have already been exerted in coming up with good designs to test. The final selection on the basis of good results is only the icing on the cake. If you test four designs that seem like good ideas, and one of them works best, then at most 2 bits of optimization pressure can come from testing - the rest of it must be the abstract thought of the engineer.

Why are we vastly better at optimization (on some problems) than our ancestors if we share the same psychology? Culture.

How is worthwhile scientific culture built up? Testing. Your car designer relies on people testing the properties of materials such as toxicity, tensile strength, melting point, chemical activity and many more. He also relies on the tests of the values of air resistance, wind tunnel simulation accuracy, gravity, likely surface friction and many many more.

The car design is built upon a mountain of tests, not many done by himself. Abstract thought can't get you very far with no tests at all.