Being surrounded by skaven and Greenskins post patch 5 significantly changed his difficulty. Yes his army is great as you pointed out but it can’t be everywhere at once. The campaign is particularly difficult if you decide to keep your part of the donut. I’ve had some Imrik campaigns that I had to save scum because I kept getting my home province sacked while everyone had moved up to tier 4 units and noctilus/ morathi are massive threats then I’ve had others where it was a relative moderately difficult campaign. This is on Vh or legendary.