...what, specifically, do you think the Struggle system is as a mechanic other than a framework to allow modular substitutions of mechanics of dynamic rule changes over time tailored to a region?
A Person struggle is not just going to be Opportunity/Hostility or Compromise/Reconciliation. It would be introducing its own phases, with their own rule sets and own transition critieria. You can see the Struggle system's flexibility with the
RICE mod's North Atlantic flavor pack, where Greenland colonization is modeled not by expanding the map, but by a Struggle system of Settlement/Integration/Marginalization/Subsistence.
Saying the Struggle mechanic should stay in Iberia is like saying the religion system needs to stay limited to Catholics.. It's a mechanical architecture, not the specific mechanics used for a specific example.