Both can be true. Events are used to keep the player in check precisely because the AI isn't up to the task.2. AI cannot handle them. People say that the crises are another way to keep a runaway player in check, but in reality the crippled AIs handle them so much worse.
Mods which disabled or delayed the end-game crisis event in Total War: Warhammer were (among) the most popular mods I published for that game. Popular enough that Creative Assembly overhauled both the campaign and end-game crisis scripts to make it easier to disable when I stopped updating my mods, and by Total War: Warhammer 3 they eventually programmed in a menu option when starting a campaign to disable (or intensify) the end-game crisis.