I think that the frequency of duds in GWX 2.0 reflects what happened in real life. All torpedoes had two pistols - contact and magnetic - which could be easily selected before firing. At the outset of hostilities, the then "state-of-the-art" magnetic pistols (Vorsprung durch Technik?) proved to be so erratic that crews switched to contact pistols, only to find that they too were faulty. The trigger prongs were too short: a torpedo often hit a ship and was deflected without the prongs being touched. The U.S. and Imperial Japanese Navies suffered from similar problems: I am sure the Royal Navy did as well. A design problem also effected the torpedo depth-keeping mechanism which suffered adverse effects caused by constant pressure variations within the pressure hull of the U-boat.
The official explanation for the failure of magnetic triggers was that they were affected by variations in the Earth's magnetic field. I should think that it is also highly likely that the de-gaussing of British and United States ships had more than a little to do with the failure rate of such triggers. Whatever, these faults continued throughout the war and were only solved after the end of hostilities.
Dönitz complained bitterly to the torpedo directorate about the failures: the directorate responded that crews were to blame. The same happened in the U.S. Navy: buck-passing.
Post-war research suggested a failure rate of 30% overall. On one war cruise the U-32 fired 50% duds. An inquiry showed that the contact pistols had only been tested twice before the war and that they had failed both times! It became clear that torpedo failure had been experienced and reported since December 1936 but nothing had been done about this. When the war made it impossible to ignore the faults any longer, Raeder demanded action. A rear-admiral was court-martialled and found guilty; a vice-admiral was dismissed from the service.
The whole story simply provides a glimpse into the sort of bureaucratic bungling that was a well established feature of Hitler's Third Reich, when party loyalty tended to outrank competence.
Torpedo failure notwithstanding, one should also realise in the interests of "reality" in a subsim that a more important, and perhaps more surprising, statistic concerning U-boat warfare is that less than 50% of all boats built got within torpedo range of a convoy: of the 870 U-boats that left port on operations, 550 of them sank nothing.
Ende der Durchsage!