Determinism(to some extent) by conditions not fate.. well written.
I will try to exemplify what you said from my perspective:
Iberians colonizing the Americas was most likely to happen. Similarly, it was not likely to happen for Muslims in Northwest/West Africa to colonize there. This statement have more than one factors(conditions) behind it like any other historical statement. Muslims living there had the access to Silk Road and Spice Route somewhat. Iberians on the other hand, especially Portuguese, were mostly poor and in dire need of a way to create income. But this was not the only reason because Algerians too were poor for instance. Lands those Berbers lived on were mostly barren lands, that is why we saw piracy here(another historical statement with condition in it). So colonizing and reaching new goods including slaves would be nice for them too. However their ships were not suitable to sail across the ocean. Iberians, again especially Portuguese living near the ocean, reached that technology with trying to sail across/through ocean for decades or even centuries. Berbers did not have that however, their focus was always Mediterranean Sea and their ships were suitable for there. Because their focus was the other side of the Mediterranean where rich lands of the Christian denominations waiting for them to plunder and ease their hunger.
Determinism by fate: Make AI Iberians choose exploaration ideas while prevent others to do that(excluding players of course, they would be pissed)
Determinism by conditions: Simply, reflect the situation over there. Make galleys not suitable for sailing across the ocean and more importantly make heavy ships an important naval technology which requires time and resource investment to reach. As a result, instead of restricting AI decisions, you can give the Iberians their exclusive ship technology from the start and sit back, relax and watch the plausible outcome to occur.
As a bonus, you can reflect other situations like Ottomans-Portuguese conflict over Arabian Peninsula and beyond on the seas as well. Ottomans were too a Mediterranean-only civilization thus their ships were not suitable for the ocean. They were indeed no match for the Portuguese on the sea. That is why we didn't see an effective Ottoman influence over SEA hemisphere not because they didn't send some money for some weird remote control over there through trade chartering.
Not just these, institutions or any other mechanic should/could be made with that thinking. In fact, Paradox Grand Strategy games in general should be made with this perspective imo. Not with a shallow sandbox aspect with gameplay over realism/history, they should put both(gameplay and realism/history) on an equal level and think both together. Because these games are not just board games but complex computer games.