Romans. They had tactics that emphasized their swords and they killed a lot of people with their short swords.
Throughout alot of the eras of the empire the Romans used spears as the main weapon.
The banded armour, big square shield and gladius era was the most iconic and hence what people think of.
Even then the spear was swapped for 2 javelins which are kind of a big deal when 40k guys are throwing them at you.