From a military point of view, there's plenty of advantages to firearms over bows/crossbows. But they're mostly things that don't matter (or at least aren't considered) in D&D.
Yeah, I agree. Most of the advantages people think of when they imagine firearms aren't that big (usually just +damage), and the disadvantages are even worse (cost, reload time, weight, reload time, misfire chances, did I mention reload time?)
I should point out that "reskinning crossbows" wasn't my idea. It actually came from my players. Apologies in advance for the long, boring backstory...
I'm running a swashbuckling campaign with renaissance technology...so we're all about flintlocks and cannons over here. At Session Zero, when I was introducing the campaign setting, the players asked about firearms--specifically flintlocks. I said yes, of course, and their response was lukewarm. Groans and eyerolls mostly. Firearms in many splatbooks and campaign books just don't work with the way D&D combat is set up and the assumptions the game makes. They are either unrealistic (I can reload a black powder weapon in six seconds!?) or impractical (I have to spend ten actions before I can shoot again?!)
I understand the temptation to inflate the stats of firearms (damage especially). Here in the 21st Century, we imagine firearms to be the best weapon possible, and so we are tempted to mirror that assumption into the game regardless of the setting's technology. But this is a game, and that inflation has to be balanced with drawbacks, and that's counter-intuitive to our modern sensibilities of "guns are the best." Unless the damage was increased to absurd levels, the crossbow was still the superior choice because it didn't have to deal with inflated cost, increased weight, a Misfire causing it to break at random, etc.
So instead of firearms, my players wanted to know how to make crossbows deal the same damage as the firearms. (Ha ha ha nope, I said.) And crossbows have thematic problems in the setting...the the idea of pirates using bows and crossbows just seemed silly, because that's not what a pirate looks like in
Treasure Island or
The Pirates of the Caribbean. Can you imagine Errol Flynn with a crossbow? Because we couldn't.
"So you want a crossbow that doesn't look like a crossbow?" I asked.
"I mean...kinda, yeah," said one of my players. "Can't we just use a crossbow and call it a pistol?"
"Done," I said. "That was easy."
So in my campaign right now, "rifles" are heavy crossbows that go BANG. "Pistols" are light crossbows that go BANG. "Pepperboxes" are repeating crossbows that go BANG BANG BANG, a cannon is a ballista that goes BOOM, you get the idea. No new stats, no new mechanics, just one sentence added to the description: "When fired, this weapon creates an audible bang that can be heard up to a quarter-mile away."
I mean, we were already going to be handwaving stuff anyway; we might as well handwave everything.