It's a bit late in development to make changes like this but I feel like the 57mm AT gun should only be an Airborne drop, and the standard US AT should be the 3" gun. Which wouldn't be as good as a Pak 40 but would be better than the existing USF AT gun.
Since we probably can't change that, the USF AT gun should get APDS ability at vet 0, so that fresh AT guns in the late game can at least be useful if fed munitions against the armor you're usually scrambling to buy it for by that stage.
