My experience with the game so far is that Japan starts with enough units that there is nothing the Allies can do to stop either an Australian or India crush move. Heck, there’s even a 40ish % chance they can take America.
However, the balance comes into play in that even if they take any of the three capitals, they haven’t won the game, it’s about VSs now. In one game where Japan crushed India, America was able to remove the Japanese fleet and they couldn’t recover, eventually losing all island territories, and America landing in Korea.
Even in one crazy game where Japan won against America in an experimental game, the UK player had taken all of the DEI, liberated China, and taken all Japanese territories on the mainland. The UK had more income than Japan, and a similar sized navy by the time Japan started to swing back West from America. They couldn’t retake those VCs on the mainland and lost.