You need to do a little research before you conclude that the weapons are "fake." All of the weapons in Secret Weapons were actually being used and tested during WW2, even though most didn't see a lot of actual combat during the war. The Germans had a lot of things up their sleeves that didn't win them the war but maybe could have had they had more time and man resources during the later half of the conflict.
Their (Hitler's) Assault Rifle, for instance, would have been a lot more devistating had they not run out of men towards the end that could have used the weapon in greater masses. This rifle was way ahead of anything the allies were using in this category. Luckily the Allies, once again, had the far superior man power at the conclusion of the war.