Guns (from a late enough period) *are* doomsday weapons, as their total dominance from the 1800s (1700s really) onwards demonstrates. See also the various colonial wars. Even light pistol rounds out-energy any muscle powered (non-ratcheted*) weapons. By a lot. Early firearms hit harder, farther than anything that came before, allowing them to defeat armor (and resulting in them displacing all other weapon systems).
Kraydak, while your observations are for the most part correct, should we really be looking at the firearms of the 17th and 18th centuries as a model for the guns of D&D. The technology and societies of D&D are primarily modeled on the on the Late Middle Ages, particularly around the time of the hundred years war in the late 14th and early 15th centuries. Wouldn't it be better to look at the early firearms of the 15th and 16th centuries for inspiration, or even to look at the very early proto-firearms of the 13th and 14th centuries?
Honestly, the firearms of the mid-1600s are not "early" firearms at all. They are the weapons that arose after centuries of innovation and development. I think the firearms of the early 1500s are a better match for D&D, since the 16th century was a time where early guns, bows, swords, and heavy armor all co-existed with each other in history. Guns of that era would have the least impact on other aspects of D&D settings.