People highly underestimate how fast you can get an F4U and still deploy flaps and how quickly it can slow down. This is deadly for planes like a ki84 that cant turn as quickly at high speeds. If you can get around in them pretty quickly, you can still follow them up and get some good hits from d500-d800. If that Ki84 tries to slow down as quickly as you, you will easily be able to roll inside them as you can slow down more quickly and you will be able to get some shots. That being said, vs a really good ki84 pilot you may have to fly defensively in order to get a counter punch reversal shot, as they will be attempting nothing but soaring high loops. I had this type of fight last night and won by good defensive flying, grannit he had more E and alt to start the fight but made a mistake trying to roll over too early rather than doing a high loop.
You really have to have some good SA in the KI84 because once those hi 190Ds and p51s come in, getting away from them is difficult and getting ganged is highly likely. In an arena full of fast fighters and "extenders" the ki84 is difficult to be successful in during these occurances.