I hear you. Now throw in every other war and you have my daily frustration with M&W cats, not only for NZ and WWI, but for all wars and countries. Most errors involve the sticker template use.
What you have to realize is that if people use the sticker, your categories do not work correctly with it because the sticker for the world wars are set up to display a category in the form of [[Category:XXX Unit, XXXBranch, World War X]], and your categories are simply [[Category:XXXX Unit]]. This makes it difficult to work the sticker and if people skip using the unit= parameter in the sticker, the profile gets stuck in the general WWI category, which is supposed to be a top level category.
Due to sticker use, the landing level categories are what you have to plan around because PMs WANT to use the sticker and the unit= creates a category.
Your container categories are a bit wonky, too, and many units are over-categorized. For example:https://www.wikitree.com/wiki/Category:2nd_New_Zealand_Division%2C_World_War_II is in NZ Army, NZ Exped. Force, and Eighth Army. It does not need to be under NZ army, as the Exped. Cat should be under the Army (or Army, WWII).