The iberians face a huge threat from melee cavalry and in particular spear cavalry rushes. The walls can prevent total disaster, but even still the Iberian player is typically left with no means to safely gather resources outside the walls.
The romans at least can train spear cavalry and use these in conjunction with wood line skirmishers.
The iberians spearmen access in p1 is a decent solution, and one with precedent (seleucids access pikemen in p1). It should be effective to avoid spear cav rushes being too strong vs iber, and leaves a window of opportunity for these rushes to deal appropriate damage.
If the iber player can leverage their walls well and get a barracks down in time, they should be well equipped to handle large spearcav rushes.