The first and foremost changes in the N1K2 is in the reduced roll rate - especially at high speeds.
I'm not sure if I remember it correctly, but I believe it now takes about more than 8 seconds for a full 360 roll at 400mph. In AH1 it was certainly not the best of performers at high speeds, but it was at least average.
Another hit was an indirect one - the changes in gunnery negated most of the 500yard+ shots that used to happen so frequently in AH1. Couple that with a wing-armament of cannons and the long-range hit capability of the N1K2 probably dropped more than 50% in efficiency, despite the huge ammo load to spray with.
This was a pretty much devastating blow to most N1K2 pilots in AH1 - their favorite tactics used to be the "mow down".
They'd climb up to 15k+, and use the alt advantage to sweep down the "layers" of altitudes one by one, using short "bursts" of speed by steep dives. With this speed they'd momentarily catch up to a faster plane within 500 yards and then start shooting.
Since the AH1 N1K2 could handle most speeds comfortably, it was very difficult to escape from a N1K2 that was fast and diving. It'd stay with most planes in dives, and keep shooting.
Since the guns hit further out, in a speedy chase a defensive jinking would easily elongate the flightpath of the chased plane, and the distant just wouldn't part. The N1K2 would be latched on firmly.
If the jinking was only slight, you'd get hit by the guns at 400~600yards distance. If the jinking was too hard, or you went into defensive maneuvering, you'd be outmaneuvered and get shot down also.
By the time the N1K2 reached deck altitude it probably would have scored about 4~5 kills at least.
However, all that's changed in AH2. A high speed chase of over 350mph and even a 109 would just roll 180 degrees and get out of the way, and the N1K2 can't follow. It just rolls too slow, even with rudder assist.
Also, a steady increase in speed and distance of over 400 yards, and a slight jinking would suffice. I've had quite many experience escaping from guys like wingzero or busa or kyle, from that 400yd distance, in AH2. I might lose a part or two, but I'd live. Were it in AH1 there would be no way I'd be able to escape that situation.
Ofcourse, needless to say the same tactic also worked for the Spit9s in AH1, which, doesn't work anymore on AH2. I'm not sure why the usage numbers are still so high for the N1K2 or the Spit9, but empirically, I've been seeing them in AH2, about half of what I used to in AH1. There just isn't Spitfires or N1K2s around anymore in AH2 (with the exception of the last-minute base defense planes, or CV based Seafires).
Also, the changes in FM effected the N1K2 and Spit9, too.
In AH1 these two planes were among the most stable. As a matter of fact, in AH1 "better turning" usually also meant "better stability" in harsh maneuvering. You could just yank the stick around with some speed and they'd pull great instantaneous turns, giving out gun solution most of the times.
Things just don't happen that way in AH2. In many cases some planes would have great sustained turn performance, but not instantaneous turn performance.
In AH1, if I was in a N1K2 or a Spit5 or 9, and I'd see a target in front of me which I almost have lead on, I could just chop throttle down, kick rudder full, momentarily yank the stick hard and would get a firing solution. Fire the shot, relieve the pressure, and the plane would be still flying. If I do that in AH2 the plane will stall out.
So, some pretty heavy changes in small details I'd say. The Ki-84-Ia IMO is superior in almost everything over the N1K2, including maneuverability.
