They routinely kill about 2-500 men PER unit in my games now, I can use them en masse to level enemy armies, regardless of armor status, shields whatever....
I've just witnessed in a game I play with a friend his 12 slinger units take out about 5000 men defending army.
They got so much ammo, they hurt so bad, and just nothing will really stop them...
I don't know how warfare was in these times, but I don't remember slingers being some kind of secret weapon, it devalues this mod a lot in my eyes.