Another problem is that Japan has a lot of good NAs to hold the Pacific. Most powerfull battleship is a nice addition to their fleet that counts two of them, kamikaze attack is a blessing against those carriers (Kill the carrier so that the defense is reduced in the following turns => -1 carrier = -2 fighters) and so is kaiten torpedo. Dug-in is not that good given the bombardment of US BB but can still make a difference.
I found that playing games with all NAs is a lot of fun and allows players to use a lot of different strategies (I’ve never seen a german player owning 8 subs except in those games :-D ).