Fantasy treating guns as a story-breaker. Why can't the knight have bulletproof mithril armor? Why can't the wizard cast an anti-gunpowder spell? I don't think a colt is enough to bring down giant dragons and such.
Historical illiteracy with regards to anything outside of a narrow slice of pop culture-depicted history. Gunpowder is balanced in a pike and shot (or Sengoku) era.
Gunpowder is invented as a hard counter to armor, but its armor-piercing capability falls off dramatically at range - you may as well ask what the EFFFECTIVE range of the armor/armor penetration is - and the reload time and generally unwieldiness of the weaponry is piss poor. Shogun 2: Total War does a really good job of conveying how muskets can coexist alongside other weapons. Bows eat them alive (outrange them, shoot faster, superior all around) until range and reload time slowly, slowly increase (particularly through repeating and rifling), and even then they still have a decided disadvantage of being a direct fire rather than indirect fire weapon, requiring careful positioning on terrain (that thing that you can't really control) to use safely, and you expect to have to withdraw them soon after using them at all. Infantry can very much overrun them. The idea of running around with an arquebus or early musket is like the idea of running around with a bazooka. It has a very specific function and even that is limited. They sit around the battlefield being babysat by pikemen, or used in tactics like caracoles where cavalry ride in close, discharge a volley and then ride off. Once the musket becomes sleek enough to be practical as a polearm (bayonet on it), that's one of the huge things that ups its power level, because then you might as well just have every infantryman be a polearm (GOAT of melee combat) and a musketeer (anti-armor specialist) at the same time. It's too powerful of a combination to really justify deploying other, more specialized weapons anymore. It has no obvious counter besides artillery (and suddenly you start to see people actually using field artillery). The only sort-of-counter is light infantry tactics, if you're not trying to hold a position. In vidya they're usually depicted without bayonets, but I don't understand why, I don't know that they didn't have them IRL and can't imagine why they wouldn't.
Edit: I looked it up and it's accurate. Early rifles were flimsy, sensitive pieces of shit that couldn't bear the weight of bayonets well. WHen I say light infantry, what I really mean is giving your expensive long-range/high-accuracy guns (which eventually means rifles until rifles become ubiquitous through industrialization) to smaller units of well-trained marksmen. Said marksmen are not supposed to engage in melee (bayonets are poo on an 18th Century rifle, the unit is small and their comparative advantage is range), so they mostly drill in skirmish tactics involving taking cover and spacing themselves out. This leaves them vulnerable to being overrun in a melee, but again, they're not supposed to let themselves get overrun, hence they're meant to either support other infantry units or kite the enemy and are hard-countered by cavalry. At range they have an advantage in that, smaller unit or not, they're still actually landing more hits than the enemy. (In Total War, which may be vidya but is a genuinely good stylized portrayal of it, you kind of learn to think of line infantry - smoothbore muskets - as "melee" in a setting where all infantry are ranged, in that they're
relatively good at melee. And grenadiers even more so.)
Keep in mind too how much traditional craftsmanship goes into hand-making rifles, also suitable for an analogue to a sword. Much more interesting than a bow.
Double Edit: The idea that guns was a major factor in conquering the Indians is common but insanity. Early on they were frequently outclassed by better weapons. (The conquistadors even found themselves discarding metal armor when faced with the Mexican jungle.) Later the Indians often had better guns than the Army. Indian defeat is more about facing a highly cohesive and relentless enemy; it's civilization clowning on barbarism through logistics and organization, not technology.
A smart fantasy writer would also recognize that powder making is a traditional craft and chemistry, ie adjacent to alchemy. The fantasy setting could as well have them slinging slugs of crystals and gemstones and exotic metals (beyond just silver bullets) propelled by magical arcane powder formulae. It doesn't have to be literal real world gunpowder, is the point.
I've thought before about the void of a American/colonial high fantasy. Not Medieval fantasy with a few cheesy/inane Western trappings, actual high fantasy built up around the themes of early America in the same way that Tolkien built high fantasy around the kind of monsters, myths, historical experience/societies that reminded Europeans of Europe. Sasquatch instead of dwarves. Thunderbirds instead of dragons. Bayonet and revolver. Republics. Ancient pyramids. Magic systems derived from the superstitious Christian, Voodoo and Indian magic systems that most people believed in well into the 1800s. I did very little work on it, but I had a setting I was chewing over that grounded its world around river systems, the Not-Mississippi Watershed, drawn from "Wicked River: When the Mississippi Last Ran Wild" (the Mississippi River is much more interesting than the West). I figured some aspects of America ought to be changed, like slavery resembling its classical antiquity form instead of racial slavery and the United States analogue being a far more chaotic/unstable place that frequently fractures and where Free States/Republics frequently wage private war, the religious denominations being blown up into properly distinct religions, and some other little changes that still preserve the aesthetic but aren't just complete ripoffs/retellings of American history.
