The exact same.
Show me exactly where the N1K2-J is winning. Maybe with flaps out, but the Ki-84 can deploy them earlier. And it has worse energy retention too, so you’re likely just getting slow faster than your enemy and they just fly out in front.
It is a whole 9kph faster at sea level. Even if I drag the Ki-43-I above its critical altitude to 6km, it is still not that much slower than the -II (still a mere ~40kph slower even though it has lost quite a bit of power) and it has every other advantage.
Including an extra 40rds of ammo which may come in handy during hard carrying.
It has worse energy retention. At EVERY speed.
And before you say it, no it won’t magically have better retention if you turn a little less, because it also just outright turns less (unless you’re above 500kph, which you won’t be for very long).
Again, why would I when I can play a similar plane that doesn’t require me to fight it at every step, which offers better turn performance to deal with pesky enemy Ki-43-IIs and -IIIs (and other annoyingly maneuverable planes), retains speed better in turns, and also just straight up looks better?
So you’re above your critical altitude all the time and you’re making even less power than the paltry 1100hp its engine makes.
It won’t make a difference.
The slower you are, the harder you have to turn to dodge effectively. The Ki-100 is quite fast in comparison, it can easily dodge most enemies in just one move.
The Ki-100 will enter those fights already at a higher speed, though. Which you will need to catch up to people who don’t just deliver themselves on a platter for you to kill them.
It is fighting 109s, Yaks, Las, the sort, which it easily outturns while not being limited to a quite light armament and ammo load nor a very low IAS limit, and it compresses less at high speed. It also runs much colder, has effectively infinite WEP, people can’t just dive away from you…
In short, it is an actual 4.0 fighter and not a 3.3 or 3.7 that was once good years ago and then got nerfed extremely hard.
Back to the N1K2-J: Ki-84 has identical maneuverability. Ki-84 has flaps than can be deployed at much higher speeds. Ki-84 is faster. The N1K2-J has better guns.
N1K1-J is slower, but more maneuverable. It has the same guns, just with less ammo. It has better performance at altitude.
Both of these are 5.3, but the N1K2-J which is even with them, gets to be 6.0.