but the axis would probably never want the US able to focus only on one theater of war
Depends on which Axis player I'm controlling.
It could be a good thing. I won't really know until I see the set up. Perhaps America being unable to aid in Europe would spell the end for the UK or possibly Russia.
Pretty sure that Larry said that a US that doesn't spend income both ways to a degree will usually result in an Allied loss. Probably Germany is powerful enough that if the US goes full steam toward Japan, then Germany can keep less men in France and bust through Russia easier.