Why longswords have 0.225 lethality?

[Ludens]

Short-swords also get an attack bonus in the EB stat system, and the Gladius Hispaniata has a higher lethality than other short swords. The only bonus that barbarians get is a +1 to armour. This was done for balancing reasons, but there is a historical ground for this. Celts were very popular as mercenaries, so it seems unlikely their heavy infantry did not deserve their name. Personally, I reason it represents individual soldiers supplementing their equipment with captured material. I doubt most Celtic warriors would choose to continue fighting bare-chested when they had looted a half-decent chainmail vest somewhere.

You can make a case that this resulted in Celtic elite units being too strong, as they would have less opportunity to improve upon their already high-quality armour, but remember that Celtic units with chainmail are not equivalent to Roman legionaries. Legionaries represent the rank-and-file equipped with mass-produced armour and weapons. In the Celtic armies, chainmail is rare and therefore reserved for veterans and elite units.

Randal, I think you are right that longswords would require a different formation. However, it's not just a question of "better". A longsword is heavier and I guess it requires more training in specialist moves than a stabbing sword. It's also more expensive and difficult to forge, and the Romans' best steel appears to have come from Iberians and Celts. Also, the Roman legions did eventually adopt a longer sword in the form of the Spatha.