Tophat, I ask a simple question: how long has humanity been around? How long have firearms been around? The Assyrians were slaughtering each other with swords in 4000 BC; fast forward 6000 years to the military application of firearms and you'd be incredibly arrogant to presume that we've killed six millennia of people in the last 300 years. If you make that argument it could only be justified by better records-keeping and awareness of the last three centuries as compared to pre-1700. The Mongols alone killed 40-70 million people during 30 years of conquest; the Qing dynasty killed 25 million when it overthrew the Ming. Those two wars equal or surpass both WWII and WWI, respectively. Now consider that there are many thousands of years more of warfare and conflict, the vast majority being waged without firearms (and many being waged to total war - think of the utter elimination of Carthage) and I dont see how you could claim that casualties of the last 300 years equal that.
Firearms are more efficient in killing people in a faster period of time than any of the melee weapons ever created. Both World Wars in the mid 20th century showed that. Firearms depending on the variation can kill quite a number of in under a minute easily. It also depends on the abilities of the user and the weight of the firearm itself.For example, an AK-74u given to a professional can instantly kill at the very least fifteen people under a minute because it is an assault rifle.
No melee weapon can be used in such an efficient manner. Nevertheless, melee weapons depend on the physical abilities of the user to wield the weapon effectively and strike/stab an opponent who is most likely fighting back. Versus a firearm which only needs to be aimed accurately to kill someone a few feet a way or a miles away.