If US goes full against Germany, Japan can threaten USA from the pacific coast or Japan can aid Europe with it’s large fighter corp.
I like the fighters in europe, easier to achieve as the ftrs have the range, japan can afford to give them away and buy additional ones.
Not sure what Germany is doing in your game as you really don’t speculate. Tanks? buying ftrs is a good move to help the defense of fortress europe and keep the allied fleet honest.