The reason you can't 2 shot tin cans is probably because of the damage value change. I personally don't recommend using the throwing lances with a mere 7 PT. In my opinion, if you are going to use such a limited amount of ammo, you need much more PT to make those shots count.
I don't shy away from criticizing the game balance team, and I'm one of the last people you could accuse of brown-nosing chadz, but I think they did a pretty good job of putting throwing in the right place.
My only question is: why the hell did you nerf rocks?