Meh, prior to 3e, that was called a Longsword. Unless you were using a two handed sword, there was no reason to ever not use a longsword. I mean, people are talking about the weapon vs armor table. Let's take a look shall we, just to refresh memory:
So, a mace, vs AC 2 is +3 better than a longsword. And +2 vs AC 3. How often are you using full plate or plate mail armored foes?
Virtually nothing in the game actually had AC's in that range. AND, virtually all magic weapons were longswords. Certainly all the best ones were. This myth that there was this magic time in the past where players chose a bunch of different weapons is just that, a myth. In AD&D, you used a longsword, full stop. There was just no reason not to use it. It was head and shoulders better than anything else.
1e creatures with AC.3 or better in the MM:
Aerial Servant
Anhkheg (main body)
Ant, giant
Beetle, giant - boring
Beetle, giant - rhinoceros
Beetle, giant - stag
Beetle, giant - water
Beholder(main body)
Brownie
Bulette (main body)
Carrion Crawler (main body)
Chimera (dragon head if memory serves)
Crab, giant
Demons, Devils, Demon/Devil Lords - almost all were well into negatives, a few at AC.0, so way better than a mere AC.3
Dinosaurs: Ankylosaurus, Archelon Ischyras, Monoclonius, Paleoscincus, Pentaceratops, Stegosarus, Styracosarus, Triceratops
Dragons - ALL
Dragonne (main body if memory serves)
Dragon Turtle
Efreeti
Elementals - Air/Earth/Fire/Water
Ettin
Gar, giant
Ghost (if you weren't ethereal)
Giants: Cloud/Fire/Stone/Storm
Golem, Iron
Gorgon
Griffin
Groaning spirit (AKA: Banshee)
Imp
Invisible stalker
Ki-Rin
Lamia
Lich
Lizard, fire
Werebear
Weretiger
Men - were listed as: ** - could be anything. Depended upon how the DM armed them
Morkoth
Mummy
Naga, guardian
Neo-Otyugh
Ogre (chieftan)
Otyugh
Piercers (all sizes)
Pseudo-Dragon
Quasit
Rakshasa
Remorhaz (head & main body if I recall)
Roper
Rust Monster
Sahuagin (baron/noble, king, prince)
Salamander (forget wich part)
Scorpion, giant
Sea Lion (forget wich part)
Shambling mound
Snake, giant - amphisbaena
Spectre
Sphinxes - ALL varieties
Squid, giant (main body)
Tick, giant
Titans - all sizes
Trapper
Treant - all sizes
Triton leaders (AC.4 or better)
Turtle, giant - sea & snapper
Umber Hulk
Unicorn
Vampire
Will-o-wisp
Wyvern
Xorn
Your right, virtually nothing in the game had AC.3 or better. And certainly nothing commonly encountered....
Would you like me to compile you a list of AC.3 or better foes from MM2 & the Fiend Folio?
As for never using anything but a Longsword? Speed factor - short swords (and daggers) were faster & faily common as magic items. Class restrictions - not everyone could use longswords....