The Iberian fighters recruitable by all Iberian factions in grand campaign use a different javelin than the mercenary and auxiliary roman version of the unit.
In turn that changes how the unit behaves:
it was a hybrid skirmisher with 5 (80 meter range) javelins that deal reduced damage like thureos spears and got changed to melee unit with 5 precursor (thrown before charge) 40 meter javelins for the Iberian factions severely nerfing them.
The unit has loose formation available so i think it was meant to be a skirmisher hybrid.
Throwing 5 precursor volleys means charging the unit into another 5 times which requires some serious micromanagement in mp
It is underperforming with the "new" javelin making iberians weaker both in mp and campaign.
The javelin it used before the change was rome_javelin_light same as the Lusitani Guerrillas (which also have 5 ammo) and all the thureos spears versions in the game.
The one it has now is rome_iron_javelin it is used by almost all melee infantry in the game.
just changing the javelin it uses reverts the changes and makes the unit identical to the mercenary and auxiliary version
I think it should be same across all 3 versions in the game.