Europeans also had writing, which enabled military leaders to benefit from a thousand years of military history.
Consider that an organized Roman legion could (and did) defeat barbarian hordes, equally armed, ten times their size. That's what strategy and tactics will do.
from your link: "More recent scholarly works mostly agree that the armies were similarly sized"
Since that battle occurred fairly late (378 AD) it wouldn't be in the least surprising that the barbarian "hordes" had learned how to fight in a more coordinated, tactical manner than a mob rushing the legions.
Consider that an organized Roman legion could (and did) defeat barbarian hordes, equally armed, ten times their size. That's what strategy and tactics will do.
Pizarro's swords and muskets didn't defeat the Inca army. It was strategy and tactics. https://en.wikipedia.org/wiki/Battle_of_Cajamarca