The reliability was abysmal even at its best. Realistically they could have improved it but not enough to make it worth producing and putting any significant numbers into operation. The fact that jets are fuel hungry hurts the Germans more than the allies, the allies had plenty of fuel the Germans did not. The Germans did indeed have to worry about fuel indeed it became a critical concern. The Battle of Britain was indeed lost in part because the fighting was over Britain but it was also a much more even contest. The jets don't have to fly close escort and there will still be piston engine fighters escorting the bombers. As it was the allies would rotate the fighters for a raid and they had the numbers to do so. Consider also that as it was the German pilot training program suffered due to lack of fuel. What happens to your training program when you start producing lots of difficult to fly, fuel hungry planes that are a logistical nightmare to keep in the air .