shoot at at a unit of peasants (0 armor) with archer auxilia. Mod in 2 hp if you want to make it more exact.

Try again with chariot archers.

Chariot archers have 2 hp, but that can't account for the vast difference in kill speed. chariot archers die at a rate far closer to units with 10 armor than 0.

I don't know the exact mechanics of chariot/rider hp/def, so I won't even guess. But I do know that chariot archers do not die at a rate even close to resembling 1 total defense, 0 armor.