I would argue that the combination of Luftwaffe directive to the Fighter arm to 'ignore' US escorts along with steadily increasing of high (er) time replacements and new units (like 354 and 357FG) enabled the USAAF to develop leadership top to bottom, develop tactics and lessons learned - then transition to long range escort in a flood.
There was no steady attrition in the early Jug Fighter Groups and for the most part, all of them had been immersed in air combat, and for the most part the LW pilot wasn't sticking around to use their courage and experience to bloody our noses and thin out the ranks.
From my perspective the single worst outcome that could have happened - did. The US fighter pilot became very aggressive and universally adapted to the mantra "Attack' - which was a very deadly combination when the fighter platform met or exceeded the adversary and the pilots now had the skill, experience and numbers to hammer the LW over Germany.
In effect, the 8th and 9th AF woke up one morning and realized "Hey, I don't have to return home anymore while you bunch up and hit our bombers. Doom on You."