This brought back some fond memories. I still remember playing in Game Workshop’s Eye of Terror worldwide campaign where you did battles with your armies and logged the results online to effect the outcome of the various planets and war zones involved. The “new” armies in this book were a nice touch from a fluff perspective but did not seem too competitive in my experience.
I do believe that this book influenced how the importance of Cadia was shaped, as well as the theme of its army. The Cadians seemed to be a thing afterward- the premier Imperial Guard army (seemingly to be more common than others, such as Catachans, Tallaran and Mordians for example).