BnZ,
The N1K2-J does not have "Ho" cannons. It has Type 99 Model 2s which are based on the Oerlikon 20mm cannon, but modified to be belt fed and have higher muzzle velocity. The last time they were tested in AH they hit just a fraction softer than the Hispano Mk IIs, significantly harder than the MG151/20s, ShVAK 20s, B-20s or Ho-5s. The muzzle velocity is about the same as the MG151/20/ShVAK/B-20/Ho-5, but the rate of fire is significantly lower than any other 20mm cannon.
The Ho-5 20mm cannon you keep dismissing does have a lighter hit than any other late war 20mm cannon, but it also has, by a significant margin, the highest rate of fire. The Ho-5 is based on the Browning machine gun design and is used in AH by the Ki-84, Ki-67 and Ki-61.