After recent trip to the U.S. Air Force museum I saw the Dora and P-51 parked next to each other, it made me wonder how the Mustang pilots had such great success against these planes. The Dora had more than a 500 HP advantage over the Mustang, but was about 10 MPH slower. The one thing I did notice is the Dora looked considerably bigger than the Mustang, which may or may not have been a disadvantage. Were the tactics of the American pilots better, was it a case of superior numbers, or was the Mustang just a better plane?
Combination of them all basically. Luftwaffe training had totally deteriorated with their fighter pilots getting far less training than an equivalent US (or British) one.
Numbers was an issue, but not until later in'44 in the sense of Mustangs.
High altitude performance was a big thing. The 190D was, as admitted by Kurt Tank, an interim design until better high altitude German engines (two stage ones) became available.
The US bombers came in high,many of their escorts were higher still, therefore fighter combat, which had been trending down after the BoB, climbed up again.
The 109 coped since it always was a high altitude fighter but it's small size prevented really upgunning it enough to take out the bombers, if it was, with gun pods attached under its wings, it's performance deteriorated so that it was very uncompetitive against the US fighters especially the Mustang.
The 190 being heavier with the BMW 801 engine suffered too. Like the British Napier Sabre it ran out of puff at the high altitudes. So the tactical environment changed and the Germans were caught short.
In terms of fighter to fighter combat, the Mustangs could sit quite comfortably much higher than the 190s, then dive down on them (a height advantage is one thing every fighter craves). If the 190As tried to come up to them, then they became uncompetitive, if the 190s tried to ignore them and go for the bombers then the Mustangs could dive down using their height advantage.
Now tactically the Germans faced the same issue as the RAF did in the BoB, but unlike the British which had Spitfires which were as good as (or close to) the 109s higher escorts performance so they could be put against them, while the slower and lower altitude performing Hurricanes could wreck havok with the bombers.
So think of it as the 109s were the German Spitfires, the 190A's were the Hurricanes of the time. Trouble was that unlike the 1940 109/Spit fighters where they were fairly equal, the 109s of the time were not equal to a Mustang at all.
Hence the 190D, which, using the analogy again, was like a Hurricane (in this role) with a Merlin XX series engine, helped but still inferior at the higher altitudes (lower down lethal though).
Now MW-50 did not help high altitude performance at all, but NO2 did. 190As never used MW-50 (they used C3 injection). NO2 greatly increased high altitude performance, though only for a time until it ran out. It also increased the weight of the planes that used it and, as the German production/transport system broke down became difficult to get.