The KI-84 is a real beast if a) you don't understand what exactly it can and can not do, and b) it's being flown to it's potential. Fortunatly the prevelance of condition a usually limits condition b.
In the MA the KI-84 has two main strengths that really make it worth trying. First when you cut throttle this thing comes to a stop in no time. Turning it with 0 throtle it actually slows faster then a typhoon. I don't even attempt medium speed reversals against this plane because of this. The other strength it offers is that it can go verticle fairly quickly at low speed. This requires a great deal of care, as it's stall isn't particularly forgiving. But its this low speed verticle performance that allows this plane to consistantly out-turn the spitV in a knife fight. You just want to immel, reverse into a scissor, rinse, repeat. When things get sufficiently slow do your immel then start a flat turn on top at ~90mph. You can push the spit out of his envelope at these low speeds and force him to break off just long enough to turn back in for position.
These strengths require a great deal of care to exploit, however. Stall fighting keeps you slow, so being successful with it usually involves staying above your enemy. You need good SA to manage the E states of every con in the sector as stall fighting isnt effective with BnZers comming in. I also see a lot of KI pilots get in trouble assuming they are in the best stall fighter in the game. Despite it's good low speed handling, the KI-84 does not match the 38 in the verticle. Performance wise these planes turn at about the same rate, and nose up about as fast. Yes the KI-84 has a slight turn advantage on the 38, but it's only about 1/4th a circle every 3 rotations. And before you gain this turn advantage the 38 will go verticle to speeds below 90mph, where the KI-84 can't follow. Basically as a 38 pilot these guys are brutal if you break out of the verticle to try and turn, but they die fast if you just take em past their envelope.
The other problem I've had with the KI-84 is that 'go verticle, hit flaps, flat turn, shoot' is really the only move you get to make in this plane. It's powerful, but it's not an options ride. I can only fly one of these things for a few minutes a tour, then the repitition of it gets to me. Even the SpitV has more tricks then this plane.
-p.