Teleporting armies were a signature of CK2 expansionist strategy. In fact, the teleporting army shenanigans were in some respects more extreme, as if you gave, say, the multi-King of all of the UK a single county in India, you could raise and return the army from the UK and India with no delay time.
This was even easier with Vice Royalties, since you'd just hand out a viceroyalty to a monarch to get the teleportation fields agoing.
Tech-rushing was even more broken in that game than in a CK3 867 campaign, but even there vice royalties were something else. Charlemagne DLC was just 2 years into it the run, and it fundamentally broke the large empire management challenge sidewise due to how it let you abuse not only opinion modifiers but teleporting the armies of a vassal vice-royal king.
I used to give my king vassals specific counties near the capitals or borders to be able to raise their entire levy in those specific spots.
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