It has been my experience thus far that it is easier to crack the Japanese nut than it is the German one.
Why? I don’t know for sure, but I have some thoughts.
1) Japan starts with 17 IPC. Yes, that jumps to near 40 really fast, but it’s still like having half a pay check and one spent on transports usually.
2) Japan takes 6 rounds to have any reasonable chance of invading Novosibirsk and Kazakh. I don’t care what your dice were, it’s still 5 rounds to walk there and you have to get through the Chinese and Russians first.
3) America has 48 IPC routinely. This can be dropped to 43 IPC but not reliably if America is going strong Pacific.
4) Japan’s basically fighting on four fronts if you go navy. They have to keep up with you, at least to slow you down. They have to take out China for money. They have to deal with the Russians from the north and from the west. And they have England from the “south” if England set up an IC in India or Australia or Egypt (I like Egypt because many Germans are not attacking it anymore and that means I can easily have 4 inf, art, fig, bmb there before Italy.)