CMV: in D&D, slings should be a Martial weapon.

In D&D since 3rd edition, there are simple weapons that most characters can use and martial weapons that warrior classes would be trained with. And sometimes exotic weapons that require specialized training and would not be known even by professional soldiers.

Now obviously, this is a total oversimplification of real life. In real life, a professional soldier specializes in one weapon, maybe two or three. A longbowman couldn't hold his own in a rapier duel, nor could a Viking warrior handle mounted archery. In D&D they can. Some editions have tried requiring specialization, but it hasn't really added much to the game. But the basic idea that a bookish wizard can't handle a battleax, that the roguish street urchin can't wield a lance with much skill... those are kinda staples that make sense both by the simulationist part of the game and the gamist part of the game.

Ok, so a sling. That's a hard weapon to learn and even harder to master. In ancient armies they were considered at least as good as bows but requiring more skill; today nobody knows precisely how good a weapon they are because we have literally zero modern slingers with even a tenth the training ancient slingers had.

Now I don't want to go so far as to say they should be considered exotic weapons. I mean, that's not really part of 5e, and even in 3e it was reserved for weird stuff like spiked chain fighting or special Dwarvish weapons humans aren't used to. Slingers would be familiar to any medieval army, and were cross cultural. D&D allows longbows to be martial weapons, and those were weapons people deformed their bodies practicing IRL. Slings shouldn't be exotic.

But they're consistently listed as simple weapons - weapons that don't require much training. That's simply false. Just as a bow requires far more work than a gun to learn to use properly, a sling requires far more training than a bow to use properly.

I understand where D&D was coming from - the Biblical trope of the sling as the weapon of a non-soldier, such as the shepherd David who had no martial training. (That David later became a consummate warrior is of unclear relevance). But, like, the shepherds did not learn the sling because it was easy. They learned it because it was cheap and highly effective, requiring no more resources than rocks, a bit of leather, and hours of practice a day that could be done in conjunction with their shepherding duties.

Thus, it should be a martial weapon. Commoners in certain professions/areas might be able to access it, just as an English Yeoman might be considered a commoner with a longbow proficiency. But it should not be a simple weapon - something a random non-martial character picks up as a default simply because a bow or sword would be too hard for them to figure out.