I worry that ideal peasants are a bit too simplistic of a measure. There are some configurations that are effectively invulnerable against unarmed opponents in combat situations and could essentially kill as many peasants as they can reach, and could, over the course of years, go through millions. Meanwhile, a very lethal critter with obvious weaknesses might be able to go through ideal peasants at an extreme rate, provided that they are not surrounded, and thus, in a one-versus-many encounter kills far fewer than a more consistently resilient unit would, but when employing formations and tactics to cover their exposed rears accounts for a far larger proportion of their team's kills.
Also there is the issue of units specifically suited to numerous but unskilled opponents. Something that effectively immune to peasants might be outmanoeuvred and pierced by trained soldiers with hard and heavy weapons, while a critter suited to killing professional soldiers with lethal hit-and-run tactics might be swarmed and torn apart by a similar number of fast and desperate peasants.
And then there is the issue of actually killing these peasants. An inebriation spell might be very good at reducing enemy performance, but not actually enough to kill anyone by itself. A wizard with Booze Cloud(an area--effect), Bite of the Paranoid Shroom(a weapon enchantment), and Spear of the Malevolent Chilli(a ranged bolt that causes pain and potentially blindness) might have a kill-rating of around 2 or 3, but might be the difference between a bunch of spearmen being overwhelmed handily or holding a pass for hours.
Then there is the matter of ammunition. An Olympic gold-medallist marksman with a rifle and 5 bullets might well be able to kill 5 peasants and then beat up a sixth with their rifle, but make it 7 and they go down in a two-to-one brawl. But those first five kills could have been something much more intimidating than a mere peasant.
Perhaps a compromise would be to have a number of ideal peasants killed with an upper limit to it, and then add a time that is required to kill them.
Or maybe the scale jumps to a new standard at certain points. Like, there is no such thing as killing 10 ideal peasants, because instead of ten ideal peasants, you get one ideal tiger, and if you are up to ten ideal tigers, then you jump up to the ideal orca scale. And, effectively, one orca is equal to one hundred peasants, but if you can kill one hundred peasants then it probably isn't the number of peasants that is the determining factor as opposed to it being a matter of getting tired and making mistakes. Orcas, on the other hand, if you can kill an orca then a second orca, or having some tigers and peasants riding on the orca, adds a lot of imminent threat beyond just exhaustion from having to stab them all.
P.S.
*Dons top-hat and carapace-wax. We shall show those barbaric peons the superiority of our superior insectoid culture! We had mastered the art of dance before you vulgar brutes had managed your first stick figures in caves and the lethal wit we shall etch upon your civilisation's eulogy shall for all time demonstrate the worthiness of our cause!