woodsThis sounds to me like an after-the-fact rationalization. The U.S. engaged in a crash mobilization of resources with the entry into World War II. The federal government didn’t do anything, to my knowledge, of any conceivable military significance regarding roads until the interstate highway system under Eisenhower, a policy that was expressly billed as defense related (in order to pass constitutional muster — kind of quaint that as recently as the 1950s we still saw some effort to find constitutional authorization for federal activities).
But even if your critic’s claim is true, in your shoes I would note that the person is evading the question. The point of FDR’s policies was not military readiness. The point was economic recovery. This, clearly, they did not accomplish.