But even without Pacific War, there is a huge lot of other wars: Japan has been trying to take down the whole of China since thirties, and taking on European colonies in the region too. Even without America Japan is fucked. If you make Japan somehow win, add all of East Asia together, and move Japanese people from their crowded islands somewhere like Western China or Himalayas. They would have insane production, if they industrialize their new territories as effectively as they industrialized their own country. But Japan winning against everyone is borderline ASB imo. Even if they win, somehow, there will be lots of rebellions and it will be hard to hold all of that territory, and then they start killing people, et cetera. Maybe they can pacify it after a few decades, but really it looks less stable than Europe after a Nazi victory.
Remove Japanese expansion, remove the need for more soldiers and people. But if we imagine that Japanese never genocided or conquered after taking Manchuria, just add the populations of Manchuria (North East China), Korea and Japan together, add a few millions to few tens of millions of extra population (depending on how extensive this population raising would be and when would they stop it if they aren't expanding), and raise the GDP of Manchuria to match the other regions.