EU1/2 were extremely railroaded into replaying history, with historical events firing even if they made absolutely no sense. Gameplay was basically a variant of Risk, because blobbing was bound to make you unstoppable. These were exactly the games which gave rise to the terms Big Blue Blob and Big White Blob. Those giant provinces also meant that in some cases it was possible to cripple a big country entirely by taking just one crucial province. For example, if player was Lithuania (or Poland) and took one specific province (Ufa IIRC, but don't quote me on it), Russia was bound to fail.
That's what you always get to hear in these kinds of arguments. It's nonsense, though.
Because complaining about railroading in a historical strategy game is like complaining about the presence of firearms in a military shooter. Of course EU2 tried to guide events along a certain path, it tried to not only start as a historical game, but also stay one.
You'd get the historical monarchs and leaders. The system tried to orchestrate everything so that the the results would remain plausible throughout four centuries. Sometimes this didn't quite work out, granted. In each game you would get a couple of events (or at least witness them) that made little sense given the context. But disregarding that, the world stayed familiar enough so you could at all times feel as if you were in an alternate (but close to reality) history setting. This was the appeal.
And if events failed, it was generally because their triggers were not fine-grained enough. AGC and EEP tried to remedy this, and they enjoyed a measure of success, but realistically, if you'd try to properly account for all possible situations, you'd need a HUGE amount of triggers/events. Maybe one day there could be a deep-learning AI that modifies such events on the fly, but human-written events went to a certain length and then called it a day, understandably.
Only when AGC and EEP merged did the accusation become somewhat valid, especially if you play a nation they focused on. For example, trying to guide Japan through their civil war in AGCEEP is an excercise in frustration where most players will at some point just throw their hands in the air and let the events happen as they happen - there's just an insane amount of railroading going on.
But this merger happened when EU2 had already been around for years.
Anyway, back to the railroading argument, this complaint was exactly why Paradox gave up on the idea of being a historical game and instead created games with a historical theme.
You can play Spain in EU2 and complain about the Netherlands revolting even though you kept the populace there extremely happy, about getting bancrupcy events from the new world even though you kept your inflation in check, about the treaty of tordesillias firing even though you conquered most of Portugal and them not having a single colony and so on and so forth, sure, that stuff sucks.
But to me, it's 1000 times better than having Algeria conquering the Balkans and becoming a major colonial power in the new world, along with Cologne and Novgorod, Tirol owning most of Italy and having somehow gotten Ireland and North England, some sub-saharan tribe westernizing and conquering most of china, Turkey trying to get to their historical strength, but being stopped in their tracks by a coalition of Austria, The Hanseatic League, Burgundy, the Illkhanate, the Aztecs and Norway, working better than the NATO would centuries later - none of which even sharing a common border with the Turks ... all on a world map that looks drastically different from the real world (border-wise), with only some recognizeable names, completely fictional leaders and monarchs .... you get the point.