I think late-game invasions fill this role, but what CK2 needs is a good AI
Late-game invasions can fill that role to an extent, but that's not supposed to be what the game is about. CK2 is supposed to be a game about managing vassals, so removing the vassal management part of the game defeats the point.
in EU4 AI can create pretty strong countries which are not pushovers like the ones in CK2
Erm, what? Have you played EU4? The AI at the stage of the game I'm referring to is absolutely a pushover. In fact, I've never found the AI to be particularly challenging at any point past the very early game (starting as a small nation).
Governing a province was a part of the career path and sure they used it too boost their power, but they key difference is that 'ministerial' positions in central government gave more power then provincial. For example in Ottoman Empire Grand Vizier had way more power then even governor of Egypt.
Basically my point is as follows:
In large centralized empire having rogue people at court should be way more dangerous to the ruler then having rogue vassals.
In fact sending people to govern remote provinces was often a form of punishment and a way to get rid of someone from the capital to diminish his influence.
This is true to an extent. In a strong, centralised empire, the dangerous people were those close to the emperor. On the other hand, when an empire started to crumble, the regional governors often took the opportunity to declare independence (the governor of Egypt did so when the Ottoman Empire began to slowly disintegrate). That was even true of empires like the Byzantine Empire, where regions like Venice were de-facto independent long before they were officially recognised as such (and, hell, the HRE in the EU era, which was nominally a single empire but in practice was absolutely not).
I do think that EU should model the power of people like the Grand Vizier better, and model the fact that being granted the Viceroyality of Iceland was often not exactly seen as an honour. At the same time, the converse was also true, controlling a large chunk of land absolutely did give you power, especially if you controlled the armies that went with it.
Fundamentally, it's a matter of the game's focus. Yes, it doesn't model the Byzantine system perfectly (or, indeed, other non-feudal systems), but that's because it is ultimately a game about the feudal system. The system the game currently has is by no means ideal, but allowing you to have 5000 count-level vassals under your direct control would be far, far less representative of how large empires actually worked.
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