The term "Rapier" first appears in the Coplas de la Panedera, a poem describing the first battle of Olmedo in 1445. It criticized the nobility and their cowardice in the fight, where only 22 people died. The poem, itself, was written somewhere between May of 1445 and 1450, certainly earlier than your statement, there. Which means the rapier, itself, was invented at some point around or prior to 1445 to be used in that battle.
And, of course, the Coplas de la Panedera is the REASON it was used as an insult. Not that pointing to the witty poem would protect you from a rapier if you insulted a man to his face for wearing it.
I also wasn't going for "This is when the Rapier was used on the battlefield" or "this is when it got the famous swoopy loops basket hilt" but when it was invented. It shouldn't be that surprising that it didn't see heavy military use until after plate armor was largely discarded, as a thrusting weapon is generally a poor tool against someone decked out in steel. However, long before then it saw use in the populace as a weapon of self defense within the well to do and wealthy of Spain. In the 1540s you'd be talking about the War Rapier which, y'know, I don't care.
Also worth noting: THE RAPIER WAS USED TO FIGHT OFF AND KILL BANDITS. Like that was a massive part of it's appeal as a weapon of self defense of the Spanish. A D&D zombie, likewise, has minimal or no armor and would be precisely as well defended from the HP damage as your average anesthetized dog. As for "Large Monsters" the Lucerne Hammer would be just as useless as the Rapier or the Longsword. If it wouldn't be used to effectively kill a hippopotamus in 1v1 combat, it wouldn't stop a dragon. (Yes, I know D&D combat against a dragon is 4 or more versus 1, but I'm referring to how long any member of the party would survive in a real fight against a large, violent, powerful animal before it turned and killed someone else. And dragons are smarter than hippopotami and also breathe fire that kills you before you get close enough to use whatever comically inept weapon your like). And no. A lucerne hammer would not protect you from a hippo.
Assuming a charging hippo, and you set your hammer to take the charge and push that 16 and a half inch long spike deep enough to wound the hippo in a serious way, you're still dead before you can do anything else. That 2,000kg animal is coming at you at 19mph or 8.4m/s. Let's say the spike MIRACULOUSLY doesn't bend under the force of this beast running at you. When it hits the hammerhead portion of your weapon, we're looking at...
View attachment 417385
347kN Each kN is 224lbs of impact. 77,728 pounds of 'weight' suddenly pressing on the haft of your lucerne hammer. 35 tons of pressure. It snaps -well- before peaking. And the rest of that force goes into you as the hippo keeps moving on it's current trajectory past the now splintered haft to where you are in less than 0.4 seconds.
And that's the BEST case scenario for you.
No weapon forged by man stands a chance against a dragon.
The point I'm trying to make, here, is that it's a poor argument to say the Rapier would be useless against a Dragon. Because EVERY D&D weapon would be useless against a dragon. And complaints about it being "Too Modern" are likewise pointless because EVERYTHING in D&D's weapon listings is too modern or too ancient to be reasonably viewed as contemporaneous. Similarly, their effectiveness is flattened so dramatically as to be practically meaningless.
The Sling was completely out of military use before Plate Armor was a thing, but you can still ping a Paladin for 1d4+Dex through full plate and a helmet because sense and reason left the building when the game mechanics landed. Grab a feat and discard your Windlass and pull back that heavy crossbow 4 times in 6 seconds. Did tridents even see military use or were they just arena weapons? Light Hammers that you could throw similarly weren't a thing. Sickles weren't employed on battlefields, either, unless you wanna try to argue a k'pinga was a sickle, but they threw those wild looking weapons often enough. Whips are just -comical- as a weapon of war... unless you're fighting with a rapier in your other hand and then it was a serious fighting style in Mexico much later on.
Anyway. Yeah. No D&D weapon makes sense against anything hippo sized or larger, but -especially- dragons.
Oh, for sure. Or a nice anti-tank rifle if you're aimed at the skull and the dragon isn't dreaming any bad dreams when you pull the trigger. But D&D's list of weapons would be useless.