Its true Germany had an efficiency problem before mid 1943 because they were too late to exert total war economy and failed to efficiently profit from the occupied territories but they overcomed when Speer got in charge of German military production.
I don't think the Soviets could have outproduced Germany had the Western Allies remained neutral. Trucks, trains, food, aviation fuel, clothes, raw materials, medicine, military vehicles etc... all gave the Soviets to mostly focus on a few production areas whereas Germany was unable to do it because of also dealing with the Western Allies. Plus strategic bombing campaigns.