The US does not have enough income to represent its realistic capablities
A real problem is that its a power that relies exclusively on transports to get to the action (japan also, but japan can build ICs on the coast, USA cant build ICs anywhere worthwhile)
Transports that need a fleet to protect them.
The best thing that could be done to help the US is to give them some extra infantry in the mainland. To ease the burden of having to buy so many high cost units.
Maybe like 4-8 more infantry.
The US really didnt have a manpower shortage, and the draft had already begun by 1940.
The 4-8 infantry would allow the US to maybe buy another bomber and Cruiser over the course of the first few turns, while still able to fill its transports.
I always feel the US shows up in a theatre with 3 units too few to really scare the axis player. They show up with enough that the axis can attack, and trade away planes for boats.
Setting back the US by a little, and the axis by a little more.
When in reality, the US should show up and the axis be very afraid to attack the US transports and fleet, and have to use its air units defensively. So that by turn 6 or so the US is the major allied agressor on the board. Not just the boogyman.