I agree with you that there are other considerations besides the money islands. If Japan is not being aggressively built against, they can get the money islands when they are done with their primary goal.
Personally, I think Japan has two choices, like Germany does. Japan can focus on India first or Australia first, while Germany chooses London first or Moscow first. It may be that one way proves easier than another. However, I hope that there is more then one way to win. This would keep the game exciting.
I think the money islands help an Asia campaign since you have to build resources for the grind. If America is not challenging your navy, then you won’t need as much money to mop up islands for the win. It all depends on how America builds. If Japan gets all the attention, I’m ok winning with the Germans.
Its just naturally easier for Japan as they need 2 fewer victory cities then Germany and Italy does.