But it's also comparing apples to oranges. Modern firearms versus knives is not the same as early firearms versus ... well virtually any weapon in the PHB....
Because he's not interested in the damage done to the human body by the weapons, which is the topic of the thread, but instead interested in proving without question that guns are vastly more lethal than any melee weapon whatsoever. I've tried to steer him back on course, directly, tried to discuss the damage shown in videos he's actively posted, himself... And he just ignores it to declare victory.
Because it's not about the damage, for him, it's about the quantity of body bags.
End of the day, if you enforce the loading property and require proficiency I don't see a problem with firearms doing significantly more damage. Crossbow expertise hasn't come up in a home game yet, but much like that feat I do have an issue with the gunner feat taking away the loading property.
If your tech level is high enough to include semi automatic weaponry (or even bolt action) I think there are some issues.