The Japanese industry could not come close to matching the production capabilities of the US, UK, Germany or Russia, but they did put an awful lot of different types into service. I would not be surprised if the Japanese had the second largest number of different types of aircraft in service during WWII after the US. The reason being the same as the US, they had two separate services with two almost entirely separate aircraft inventories between the Imperial Japanese Army and Imperial Japanese Navy.
Given all of that, it really is a shame how narrow the Japanese planeset in AH is.