It just means, IF
#1. 10 min dmg - 20 max dmg = 15 average dmg and a succesful hit is guaranteed 10 min damage
#2. 19 min dmg - 20 max dmg = 19.5 average dmg and a succesful hit is guaranteed 19 min damage
over several hits #2 will win
So you're saying a weapong with higher average damage is better than a weapon with lower average damage? I'm gonna have to run some simulations, I don't know if you're right, but it'd be huge if you were