Not true. The Iberians had clashing border claims, small enough that no province is even remotely representative of the 'skirmishes' between them that resulted in adjusted borders. Hell, these border adjustments were usually the result of an external war where they were co-belligerents on opposing sides.The Iberians never went to war with each other in the EU4 timeframe with the goal of conquering sizable chunks of land from the other. The Iberians went to war with each other when there was a chance to play the dynastic game via military intervention. If anything the game needs to give the Iberians more chances to play the dynastics game.
I know we're getting a Castillian Succession crisis but I think I'd rather it be an event chain driven war between Aragon and Castille and Portugal and Leon with Leon and Castille representing pro-Portugal and pro-Aragon nobles(as the war historically went) for the potential of a Portugal-Castille PU, a Aragon-Castille PU, or a compromise peace that results in Portugal-Leon/Galicia/Sevilla and Aragon-Castille/Navarra/Asturias. I'm going to be disappointed if Portugal still doesn't have an option to do anything in the Iberian Wedding; heck, historically it was Portugal arranging the 'Iberian Wedding' with Aragon as the interloper that enforced a victory via intervention. Give all the Iberians historical friendship modifiers as well as a generic 'PU intervention' event when one of the states has a weak heir or no heir. You want Iberian wars, well this is how Iberian wars tended to go unless they were cobelligerents on opposing sides.