Japan I-400s should act as normal subs during the defense, so their fighter loaded on them will act as cargo /like any other/. The way it is now, you can buy two subs for 12 IPCs carrying (did I spell it right ?) 2 planes with attack value of 4, defense value of 2 and and you need two hits to kill em both, not talking about they roll 4 dice during convoy disrupt.
CV costs 2 IPCs more, doesn’t roll any dice during C. Disrupt, has 4 less attack power. The only things that CV is better in are that they can repair one damadge and they can carry one Tac. And last but not least, you need a destroyerto attack subs if you don’t want them to simply submerge.