I don’t think using gameplay as a basis for these kinda arguments is a super solid idea, it’s not like humans in AO are casually tanking bullets and instahealing, that’s just so that the gameplay isn’t a pain in the ass. Also modern military weaponry is a lot stronger than flintlocks/muskets so even then they would still do a lot of damage.
Plus Vetex has stated that apparently even the PEACEKEEPER can be hurt by guns (probably only if they’re not defending against it). From the discussion from Would the Peacekeeper be able to survive everything humanity (irl) throws at them?:
I’m assuming that while humans in AO are more passively durable, it’s mainly their magic defenses that actively shields them (if you ask about non-magic pure builds I got nothing lol). Of course elemental curse users are a completely different story but hey maybe you could melt down arcanium weapons/armor and repurpose them into arcanium bullets?