Update: Chaos proper finally showed up in the form of Archaon and that Ever-Watchful guy. Suffered a real bad loss to the latter one which chewed up a pair of armies, but after that the AI's strategic weakness got put on display; rather than blitzing to my now-undefended nearby provinces, they dicked around, sieging and unsieging a nearby Nordland port and finishing off Kislev, which gave me the time I needed to march up my third pre-upgrade army (I was holding Franz and one more back in Reikland to fully upgrade) and rally the other Imperial province into the area. Archaon tried to solo siege Wolfsmund, and I took the opportunity to crush the life out of him. Didn't even have to fight it manually, one autobattle and he was done. AI needs to learn when to fold 'em. Assassinated the Ever-Watchful a couple turns later too, and crushed what was left of his army.
Meanwhile, in the South, I got roped into the Dwarves' wars against the Wood Elves and the border princes for some goddamn stupid reason, and the Elves marched into Wissenland, so that slowed down my army building. Trapped and destroyed Durthu, but for some misbegotten reason Orion decided the smart play was to run over to Western Sylvania so I gotta put out that fire at some point. Wish he'd just accept my damn peace offer. He stopped fighting the Dwarves, just go away and let me handle what's left of Chaos.