Well, he would have been right a couple alphas ago. And, he was mostly right about what properties to change. So I don't want to say his info is "wrong," just not completely correct.
Speaking of not entirely correct, there is another place to look that I forgot about. If you look in NPC Core's entityclasses.xml, you'll find an entity class called "npcMeleeTemplate". That is the template used by most non-hirable NPCs.
In that template, there is code to adjust the damage modifier according to number of kills, day/night cycle, and biome. (In my copy it starts on line 391.) You might want to also mess around with those values.
If you want a general reduction in damage for every non-hirable NPC (ranged or melee), there's also an effect group in that template called "ReduceDamageToPlayers". You could make the "DamageModifier" value be a larger negative number, so they will do less damage to players (and players only).