This is not really a reasonable assumption, though, because theres multiple scenerios in real life history where countries have conquered entire regions in one go... the Ottomans conquering the Mamluks, the Timurids conquering India, the Manchus conquering China... Then you have the various Napoleonic conquests.
...and even then, EU4's maximum warscore limit of ~15 basetax is really, really, really low, and makes it hard to even hit 100% OE if your fighting smaller countries or coalitions.
The Ottomans were widely seen as liberators of the people against a foreign ruling class, and they were quite hands off with Egypt.
And the Timurids/Mughals were far from a clean conquest... they shored up each conquest with royal marriages(even to Hindu nobles) and ran something closer to the Holy Roman Empire than France or Poland.