[TW:W] How to survive the Green Doomtide?

Okay so, Chaos has never been an issue to me. You get some handgunners to pierce dat' dank armour, some Reiksguards to rout all northern "I want a new country"-beardos and let mighty King Karl take their generals out.

The Orcs however, fuck me up. Currently I got 7 damned full stack armies just south of Grenzstadt about to stomp my Empire just like the previous two attempts at VeryHard.

It's turn 158 and I've almost beaten Chaos back together with Marienburg who controls the other half of the Empire. Every single faction besides dat danky Archeon, Mannfred hiding down with the Border Princes and the Doomtide of Green Death are my besties.

There are SO many of them. Do you guys have any ideas on how to beat then and why they get so ridiculously strong three games in a row?

Not complaining though, this campaign is really, really intense.

TL;DR: Doomtide of Green Death, how to beat? They keep stomping the world.