The USofA was just too much of a world superpower with untouched economy, untapped reserves of manpower, material, resources and workforce, they could take on any single other nation at that time.
Germany jizzed their pants when they had 2 proper battleships.
America lost 8 BBs in Pearl and it didn't bother tham at all. The only reason they only had 18 battleships at the end of the war was that they shifted focus to carriers.
Speaking of which, Japan was proud of their 4 fleet carriers, but after losing them they couldn't replace those losses.
Meanwhile America could pump out an aircraft carrier every month.
Not to mention all the arctic convoys they were sending to Russia that helped them hold the eastern front.
There's this greentext about american logistic might in the atlantic and how many pounds of ice cream they could and did supply to the fleets.
If that's some civ-style game where America is just a nation with a set of bonuses starting from scrap, then ok. Slap on economic boosts, isolationist tendencies and democratic government and you're good.
But if the game is a WW2 grand strategy (anon, just admit that you're talking about HoI4) then there's no way you can nerf a caountry of this size, this population and this industrial potential to a comparable level.
You'd have to go apeshit with other nerfs. Or give them much biggere enemy, like all of Europe at that time.
Or just do what Kaiserreich did; divide them into pieces.