On this specific point, GWX is not doing the job neither even if it s actualy realistic.
The main issue in GWX is to get out and in of your home base and even this can be done much more easily if you re playing safe.
Canavaro point is you don t have to take risk to make your way to the top sunker of WWII as you can take your time and choose your target wisely. To make it challenging as P_funk mentioned it, you have to give yourself some objective. As a specific convoy, as gibraltar, as raiding scapa flow, etc...
There is no "no pain, no gain" in SHIII, even with GWX, you can always play it safe.
Actualy, I think the best way to make it more challenging is to disable map information about other ship
(god eyes or something like that)