German pilits were required to fly a lot more sorties in a day than their allied counter parts. When the war became desperate for them, they flew even more. Also, many German pilits were assigned to the Eastern front where the nme were plentiful, and less skilled, and flying less advanced a/c. Once the Russians began to produce more advanced a/c and trained their pilits better, the Luftwaffe began to lose a lot of pilits, many of whom were their best.
Early in the war, the Germans had one of the most formidable a/c, and allied a/c were simply no match for the a/c they put up.
The air war in Europe was as much a technology race as it was a fighting war. There were certainly exceptions though, and Germany had some very talented fighter pilots.