Against the Ki-84:
-Good first turn to avoid the shot. Maybe a little late on reversing your turn to create and even bigger problem for him and gain a slightly better chance of a snapshot but you still avoid the shot.
-Good job realizing you would never catch the Ki and he'd just have to rope you for a kill. Climbing away from him to gain alt was the right decision. The Ki makes a huge mistake extending for so long and letting you get altitude.
-Second merge was very good, good positioning. You didn't waste your speed trying to climb with the Ki84 and you timed your defensive turn nicely waiting for him to commit to the attack. Perfect defensive move as well, reversal was timed perfectly.
-Two missed perfect chances to get a kill as you missed the line up on your first shot after the overshoot, and then again as the Ki makes a mistake and doesn't use his superior climb rate.
-You did get lucky that he tried to reverse him turn and you got the killing shot on him. A Ki-84 would have out matched your P-39 on the deck. What I would have done is level off when he dove away. If he's going to give me the altitude advantage then I'll take it
. Then I would wait for him to either try to climb up to me and I could get a shot or try to rope him. Or I could just stay above him until he takes himself to the deck and then I can BnZ him. Diving down after him wasn't a wrong choice, but eventually the fight would have gotten a bit more difficult for you had the Ki-84 gotten you to bleed your speed off.
Against the La-7: (starting at the 8:11 mark)
-Good first turn, creating horizontal and vertical separation, nicely timed reversal but then your turn gets too flat with the La and he almost gets a shot on you (luckily he's very jerky on the controls and misses.) I would have gone more wings level and into the vertical. This would have put my lift vector further behind the La, gotten me more inside his turn, bleed some speed, and he would have overshoot below me. This would be perfect positioning to use hard right rudder and nose down into him for a shot.
-Now you get into a bit of a rolling scissors fight and your lift vector is way too far in front of him. This gets you to overshoot him and he gets another 2 shot opportunities. The first he misses and the second he just can't quite get his nose on you.
-You do exactly what I would have done now and stayed below him, cut throttle, and keep turning into him. This way when he does commit to an attack he will build up some speed in his dive and we will be turning into him creating those horizontal problems for him. This does work and he does overshoot briefly but he recovers from this by using his better climb rate to get above you again and out of your guns.
-Now comes the tricky part. You want to stay right where you are and either wait for him to make a mistake or you can somehow get to his altitude. This won't be easy though as he does have a better climbing plane. If he uses that climb rate he can force you to use up the rest of your speed trying to climb with him, or wait until you break off as your forced to regain speed. The La does make a mistake though by not using his climbing advantage and you get the kill shot.
Your weak points that I could see from this film are:
Your Gunnery - You should have at least hit the Ki-84 on those first two shots. Be steady on the controls when lining up those shots.
Rolling Scissors/Lift Vector - The rolling scissors against the La was where you appeared to struggle the most because you were trying to turn into him for a shot rather than to get behind him. This put your lift vector in front of him and forced you to overshoot. Remember to put your lift vector behind your opponents 3-9 line to get inside their turn, gain their 6, and force the overshoot. Putting your lift vector in front of their 3-9 line will help you cut the corner and close distance on them but puts you at risk of overshooting as well if you're too fast or can't turn tight enough to stay inside their turn.