If it can pen all the shots the 57mm has the highest dps for any AT gun in the game. If you are playing against medium tanks like what USF and SOV field then you will almost guarantee penetration on every shot so it is much better than a pak40. On the flip side the pak 40 is better in allied hands because it can pen the heavy armor of axis tanks better. It's nice this way, it's always better to steal enemy equipment.
lol it wud be much better if allies were given AT weapons that were on par with the axis ones that way it will be a level playing field