Quote Originally Posted by Simon Appleton
CA said that light and heavy weapons have no difference in effectiveness - it's just a tag, probably used for sound:

https://forums.totalwar.org/vb/showthread.php?t=39668
Actually, it's not used for voice, there is seperate tag for them (which also has often heavy or light in name).

But, it is used when AI decides their building preferences, as well as when assigning formation in battles.


Also, that tag has nothing to do with heavy, light weapon description that can be seen in unit cards, and is used only for weapon upgrades.