The Islamic control over the Eastern Trade in Europe affects every single country in Europe, not just Portugal. And it did so for several centuries before.
Portugal didn't pioneer overseas expansion when they did just for that simple reason, it was for a number of reasons.
And besides, their overseas expansion was more than just looking for a trade route to India, just look at the conquests in Morocco, the Conquest of Ceuta took place before any naval expedition to explore in the Atlantic, there is no correlation between wanting to circumvent the Islamic controlled silk route (which they did unambiguously want, I'm not disagreeing with your analysis, I'm just saying its too simplistic) and taking Ceuta.
Also, it was undoubtable that the Portuguese had hit a hard glass ceiling in regards to European expansion, this is not Eu4's depiction of history, this is a fact. You must be delusional if you believe Portugal could simply go on a conquest spree in Iberia after the "Iberian wedding", in fact just look at history itself, from 1071 to 1471 Portugal waged a dozen of offensive wars against Castile or León and then as soon as the Crowns of Aragon and Castile united under marriage in 1479, never again would Portugal ever attempt an offensive war against Spain (and for good reason, they were outnumbered in Population 6 to 1, and Spain often had far more valuable allies such as France). There is no two ways about it, they were trapped in the corner of Europe, the only options were Overseas expansion, or "becoming Spain's Scotland" if you understand what i mean.