And the earliest handguns appeared in the late 14th century.
Here's a pretty neat little record of armor with dates.
http://www.themcs.org/armour/14th%20cen ... armour.htm
You can see that what D&D calls "plate mail" doesn't show up until 1346. Which right around the time you get people shooting cannons and whatnot at each other.
I guess what I am saying is that it's perfect valid and fine to say you don't enjoy it in your games, and that it doesn't fit your ideal of the genre, but to claim it's not in the genre at all is just false. It exists in Appendix N, it exists in D&D, and it exists historically, so it's definitely in the genre.