The Hussite wars, which were prompted by the petitions of Jan Hus for reforms, were the first major war to see mass use of firearms, and well, they are hinted a lot ingame. But a reason I would love to see early matchlocks and firelocks in KCD is because it was a very important part of Czech late medieval warfare, and even more, a very common practice of war in Bohemia and Hungary. Well, they were never meant to be much accurate. They were also highly inaccurate, since rifling wasn't invented til about 90 years later of the game's timeline. Last time I checked many of the gunners was harmed if not killed because of exploding guns, and it wasn't a very popular (in the sense of being liked) thing to use. The guns in 1400 was unreliable and deadly for the user. Look more at a tube made by a blacksmith that had heated a sheet of steel and bent it into shape.
However the Musket is way to advanced and high tech for the time period. It was actually starting to become a thing at the time. It was more a rich man's toy, and used for bodyguards and such. Somewhere between 1400-1500, but wasn't too popular due to expense and maintinence. I'm not exactly sure when the wheel lock came out. But a lit match (slow match, think incense) was a serious handicap for anything but straight battle. Matchlocks were okay, as long as you used caution while loading. That was the early hand gun and matchlocks. Timing was right to have matchlocks, even wheel locks.