Maybe you should read a little more. Submarines (U-boats in particular) would spend days stalking and eventually attacking convoys. You really want to spend days stalking a task group? To add to the level of comparison, the task groups in Aces High travel at 50kts (verified through the AH FV by an aircraft sitting still on the CV). Although this is much faster than any task group in WWII, the task group is still much faster than a submarine which will pull 18kts at best.
Please, enlighten me. If submarines played such a good role in WWII, name one occasion off the top of your head where a submarine caused an astounding upset in the outcome of a battle or the entire war.