Yes you’re right about japan shuttling units from Japan into mainland Asia. Yes this will work, but only if Japan is left alone to focus completely on invading Asia. If the United States and Britian keep the japanese fleet busy in the pacific and apply pressure on them by taking islands, Japan has to respond to that.
Tell you what……pull your Japanese fleet to Japan and focus on shuttling units to Asia. Leave your islands like borneo, east indies, and new guinea alone to be taken by britian and the US. You’ll lose 9 ipc’s and you’ll lose momentum with your offensive. If the allies aren’t working together your plan may work. I have played against this tactic and it doesn’t always work. Japan usually stalls out. However, when I play with Japan, My first round purchase is 1 IC to be placed in kwantung, 1 transport, 1inf, 1 art. my turn 2 purchases are 1 IC to be placed in Manchuria, and 3 tanks to be placed in kwantung. Turn 3 I purchase 6 tanks. Now I have plenty of aromor to use and my range has increased. with a constant flow of tank each round I will be able to outproduce india, and break out all over Russia. My japanese fleet would just be protecting my interests in the Pacific. Transports are great, but it is expensive to maintain them. getting a beach head and building there is best, and you can still shuttle units with your transports.