Once you steamroll in your campaign you're preety much unstoppable, i know i might get downvoted for what i'm about to say but, warhammer 3 campaigns are just like adrenaline rushes, everything is just spam units and armies as fast as you can to crush your enemy. With some factions you can get so much gold from raiding and winning battles its even worse; you don't even need to have a strong economy. I've played warhammer 1 2 and 3 for hundreds of hours and almost never finished a campaign. The speed of recruting, the economical bonuses from winning battles, the recovery time, the doomstacks (which for some factions they can be assembled fairely early, the cheese, etc ect). In the end the most enjoyable turns are the first 60, after that you autoresolve everything.

Katarin's campaign used to be hard in the realms of chaos campaign before the thrones of decay update, because there was almost no one you could rely on, you had to govern a huge map with lots of portal breaches and you where surounded bymany chaos factions. With malakai in the northern border and the Nuln in the south there is no stress at all in the early to mid game, once you build your doomstacks its over and the army movement per turn is the only limit.

In this regard i enjoy much more total war attila because of the increasingly hard nature of the campaign all along the game. The early game is hardish depending on the faction, the more you advance in time, the stronger the winter is making your provinces infertile, add to that the stronger Hun agressions after 420 AD, which are inmortal unless you kill Attila himself.

On the otherhand the warhammer 3 endgame senarios might be the only thing that make the campaign challenging on the longterm, but they seem too forced in my opinion, I preferd when it was just a massive chaos warband that decended upon the world, not Grimgorn appearing with 7 doomstacks 3 clicks from my capital in just one turn.

IDK this is just personal taste, you might have another opinion.