It looks like Gla­d­ius is a Short Sword with “Addi­tional +1 Thrust DR against armor.“
I won­der does it means Gla­d­ius is a bet­ter sword than Short Sword?

First of all wel­come to the forum,Gibea.

The please excuse the late reply, I have been away for a week on a con­ven­tion.

And, finally, yes, the gla­d­ius is a supe­rior kind of short sword. If you want to use a generic short sword, you might just as well use a gla­d­ius — it is as good as the generic short sword at slashin, and bet­ter at cut­ting. But it is of course depen­dant on the gla­d­ius exist­ing.

The gla­d­ius is the result of a long tech­ni­cal evo­lu­tion of the generic short sword being adapted ever more closely to a spe­cific style of fight­ing, namely the closed rank fight­ing of the Roman legion with its heavy empha­sis on thrusts over cuts. Still, the Romans man­aged to opti­mized the gla­d­ius for thrust­ing with­out sac­ri­fic­ing cut­ting capa­bil­ity.

Over time, Roman mil­i­tary doc­trine changed. The empire on the defense had to focus on highly mobile rapid response units that could be trans­ferred to quickly to the­atres of war — cav­alry. With cav­alry becom­ing more impor­tant, infantry did byde­fault become less impor­tant. Train­ing of the the majoirty of infantry declined, and most units becom­ing a kind of mili­tia. And this mili­tia lacked the the reg­u­lar drill to coop­er­ate closely in tight ranks, and out­side of tight ranks the thrust­ing type of sword­man­ship was not as effec­tive any­more.

What’s more, crack infantry units were often bar­bar­ian mer­ce­nar­ies who had received their weapons train­ing in their native lands, where longer swords and cut­ting were the rule. Becom­ing Roman sol­diers, they did not only bring their pref­er­ence for longer, swung swords, but were actu­ally more effec­tive fight­ing that way, the Roman one being alien to them. And with crack infantry units using the longer swords, the grunt infantry units fol­lowed suit. Mil­i­tary par­a­digm changed, the short sowrd fell out of use, wasn’t pro­duced any­more, and the details of tech­no­log­i­cal sophis­ti­ca­tion of the gla­d­ius for­got­ten.

Some regions of Europe had alwys been using short swords, but unin­flu­enced by the Romans and unaware of the sophisit­ca­tion of the gla­d­ius. When areas of the for­mer Roman Empire turned back to also using the short word once again, they were unaware of the excel­lence of the lost and for­got­ten gla­d­ius, and their dif­fer­ent mil­i­tary needs never led them to rein­vent it.

And that’s why the gla­d­ius is the bet­ter short sword. It just would not exist in most set­tings. Only set­tings with a strong and long stand­ing tra­di­tion of heavy infantry fight­ing in dis­ci­plined, tightly packed closed ranks against foes who mostly aren’t heav­ily armoured could rea­son­ably have devel­oped it.