mostly the weapon name that they use is the name that's from some legend and mythology

just like Hyperion that's Seifer's Gunblade and also from mythology
in FF IX which weapon that's named after mythology? (only counted sword name)
1.Sargatanas
2.Excalibur(already in used)
3.Masamune(already in used)
4.Ragnarok (already in used)

and that's why they use Sargatanas ,
Sargatanas is the name of demon in mythology which he's the underling of Astaroth

Aegis is a shield in many mythology and appear in many FF series
Gungnir is a spear of odin and appear in my FF sereis
Hyperion is one of 12 titan in greeks mythology and appear to be Seifer's Gunbalde
Ridill is weapon that appears in Norse Mythology, possessed by the dwarf Regin.
Balmung is the name of the sword that Sigurd (Siegfried) used to kill the dragon Fafnir
Durandal is the sword of Charlemagne's paladin Roland in the literary cycle known as the Matter of France. ( appear in FF X , XI , XII )

and yes Sargatanas first appear in FF IX