The game is clearly not balanced no matter what round the Japan attack. The only win we have had as allies, was when Japan waited til turn 3 and also suffered from bad dice, UK got rich and he was never able to break India.
The balancing issue could be easily adjusted in my opinion. What were the gamedesigners thinking of giving Japan that air-armada? Japan is able to overwhelm every UK/China attempt to make a stand with some ground troops and 10+ planes and Japan has plenty more for eqiupping new carriers and safeguarding Japanese homeland.
I think that removing 5-6 planes from Japan could make the game a lot more balanced.