At least with the Chaos Invasion in Warhammer 1 and Mortal Empires, Chaos spawns in a specific area and then moves toward your territory, like the Huns in Attila. There is also the unpleasant stress of seeing 6 enemy army doomstacks spawn in your own territory that nothing prepares you for. That happened in my first Vortex campaign with Kroq-Gar, I realized I was not ready (I didn’t have Kroq-Gar ready with a doomstack) and had to reload a save to better prepare. Others post about how they were not ready for the final victory condition event and lost or had to load a far previous save file to prepare better.
I have seen a large number of Reddit and other forum posters say they hate the Vortex campaign or they simply never play it because there is Mortal Empires. Guide to Eye of the Vortex Campaign Reason for Guide The Ritual Process and Intervention Armies.