They aren't OP, they are a frustrating game mechanic.
You don't need time to tell that this is the only infantry grenade ability in the game that auto fires and you can't aim. It doesn't reward skilled play from either the usf player OR the axis player.
Make the ability cheaper, make it a free targeted ability once unlocked, give it a 15 second cooldown.
Suddenly it's a good ability that rewards skilled USF players instead of relying on the whim of where the ai shoots it. It will also become less frustrating for the axis to play against.
A grenade volley kind of ability. Sort of the assault grenades but weaker and longer ranged.