Having played a Nurgle IE campaign recently, it's abundantly clear that parts of it are designed around the Ursun campaign - the order of the "strain" techs that improve your settlements in certain climates are mostly redundant.
The first few that you can access (until pretty deep into the campaign) are Chaos Wastes, Frozen, and Temperate climates, which all feel like a waste of time when you start in jungle, wasteland, and mountains. It may be better to move all of these techs into a separate line below the core tree that you can pick in any order you like, which allows for more flexibility in both the current campaign and any future Nurgle lords that may be coming later down the line. This does cause problems for the "7 techs every tier" design though, so maybe a simple re-ordering is better in the meantime.
The same problem applies to specific racial techs - it feels pretty bad to have a Norscan tech sitting there when you may not meaningfully encounter them all game.