FTDeep, you made a few critical mistakes in the F4U duel.
Furball was able to get lower than you. When you merged, Furball was already about 20 degrees nose up. You were about 20 degrees nose down. Thus, Furball already had a 40 degree advantage. However, you added to this by beginning you reverse far too late. When your nose was horizontal, Furball was in the vertical, a full 90 degrees ahead of you. He needed only to go another 90 degrees in his immelman, while you were just beginning to reverse.
If you examine the image below you can see exactly how he beat you. More than just beat you, he was literally waiting for you....

In that second film, you reversed downward and rather late too.... You basically set yourself up to have Furball on your six in a blink.
I suggest some dueling practice with someone who does it often. Dueling is a skill not acquired in the MA.
Some simple advice.... If you find yourself in a diving merge, don't reverse immediately as you'll provide a nice fat target. The other guy will always beat you on the reverse. Extend out 1.5k to 2k and then reverse into a second merge.
My regards,
Widewing