How so? Its a very strong plane.
KI-96 pilot here. they’re an alright aircraft right now. It is still absolutely capable if flown right, and fortunately, it still retains its ridiculous climb rate (at some maps with higher interceptor spawns you can reach the stratosphere (6k meters) in 2-3 minutes. the 37mm is much worse than it used to be though. It isn’t really reliable to 1-2 shot or even crit small fighters anymore. I wouldn’t recommend to fight P-51s in it, however P-47s, most Yaks, Typhoons and the allied heavy fighters are good targets.
Still it has potent firepower. I do have a rather bad K/D ratio with it because of XP-50s, which can slightly outclimb the KI-96, as well as having that slight extra edge in speed, maneuverability, and a big edge in firepower.
TL/DR still good (enough). 37mm nerfed to hell. XP-50 at your altitude or higher is imminent death. don’t fight P-51s without good energy advantage.
In AB I would like to nominate the Ki-61s and 109s.