The Brits have humbled me!

[Myxale]

To be honest your encounter with the brits, is fairly realistic.
A U-Boot was never a Flak-boat. Since it lacked speed and armor. The outer Hull of a boot was very thin.
A U-Boat is really weak when it comes to hard on hard. Wasn't build for that purpose. It is after all a Silent Hunter

The german were desperate having to face the closed gap, over the Atlantic.
And the Total air control of the Allies.
The flak and fancy cannons were only a poor attempt to keep their dying fleet alive.

But more cannons and conning tower with larger wintergardens prolonged only the dive time further. So you action packed partol was a normal day at work.

Keep in mind, that later in war, the statistic said that form 10 boot's sent out on patrol, only 2 will return.

So keeep on suffering Herr Kapitänleutnant