At the end of the day, if you want realistic, build a time machine, travel back to 1939, defect to Germany and become a U-Boat commander.
Now, within the limits of the game code, one must balance the relative easiness of the Happy Times with the real difficulty of 1944-45. This is just a headache waiting to happen and has been attempted by every mod team ever to adjust the sensor values of the AI. This particular area of SH3 has been debated & tweaked since it's release and anyone could argue points for any way of doing things.
However, the AI sensors in GWX may be hard but they are not unbeatable and certainly are not unbelievable at any point in the war.
There are many factors that are changeable within the sensor files however, changing a single value by +/-0.1 could have drastic effect elsewhere in the game. At the moment GWX has a good balance. For example, you may find in 1939, a really n00bish escort but the next day you may find an elite escort and get sunk. It happened like this in RL.
The sensors are also like they are for another reason. GWX has always strived to reduce the amount of tonnage/renown that can be sunk/awarded averaged across patrols. The easiest way was to improve the AI detection routines, a sort of '2 birds with one stone' choice. Infact, since the advent of GWX 1.0 reported tonnages/renown award (when playing as one should) has dropped considerably. At the moment, 50000 tons is an excellent score, whereas 15000 - 30000 should be the norm.
Lastly, just to clarify. This is a game. It is held back by the original coding. If it wasn't you could bet that someone on the GWX team, would at this moment be calculating whether a butterfly flapping it's wings in Timbuktu would cause the approaching DD to detect you.