I understand what you're saying though, it kinda makes you wonder why sword is still called a sword in Eora, or why a knife is called an knife, axe an axe, etc but why gun isn't called a gun. I mean... the world of Pillars is already so complex, we have to relearn things and are introduced to many more so learning a new term for "gun" is just another thing I suppose.
Well but they are! Long sword, saber, rapier, estoc, katana, morningstar are all weapon which were used historically, however due to being more used in popular culture people are more familiar with them. I know that I had to expend my knowledge of white weaponary when I started to play RPGs.
I have little interest in firearms but I imagine that firearms used in 17th century existed before “guns” were created. I imagine that if we would continue to use swords to this day new terms and types of swords would be created. As it is now new guns were developed, while white weaponary remained mostly the same (beside combat knives etc. Used as a tool or support weapon, rather than main one).