New allies mechanized army rebuff

In ww2, U.S army has 100% mechanized army with the British close behind while the German Army was amazingly less than 20% mechanized, relying heavily on horse drawn artillery and supplies until the war’s end. The backbone of the German logistics was the railways which could only take them so far. US industry was able to produce the large volume of trucks, jeeps etc. needed for the logistical requirements of moving armies while the Germans vehicle manufacturing capacity was far less and continuously diminished by allied bombing. I have read that German POWs captured at the Normandy invasion were astonished that no horses emerged from the US landing craft and openly commented that the war was lost due to Allied forces being totally mechanized and not reliant on horse transport. So, why not give some bonus to allies mechanized unit by giving less cost to produce, giving 15% speed which help the allies which has -10% speed because we don't use majority of our time producing and using mechanized army to attack the enemy force during the game.