I agree that the air traffic is a little bit too dense in the early stages of war with OHII but on the other hand without it, it would be too easy for player to score unrealistically high tonnage . It's really hard to simulate fear factor in any game so maybe it is better this way.
And it's really not that bad IMO...Most of the time when your crew report aircraft and again few hours later, and again (and again

), it's the same plane, patrolling the same area, so it's natural for you to get the impression that sky is full of planes.
During the night or when is foggy or cloudy, planes will just fly over you and you wont be spotted.
You should know also that when you send any radio message or you have been spotted by some unit (plane or ship) all nearby aircrafts will move in your direction.
So step beck a bit captain, take some distance form the British coast and maintain radio silence...