One thing I really hate when I unlock a tech is designing units. Some people really enjoy this and others frankly, don't. One of the reasons I don't enjoy it is because I have to create multiple copies of my units for the AI to utilize them.
This means I have to create: Archer, Horse Archer, Warg Archer, Armored Archer, Armored Horse Archer, Armored Warg Archer, Light Archer, Light Horse Archer, Light Warg Archer: This will give me several copies of the SAME UNIT. One with leather only, one with "upgrade armor", then one of each for Horses, and another of each for Wargs.
This headache could be reduced by allowing nonmounted units to mount with an Upgrade button. You have finally added weapon specified upgrade chains so my Axeman won't be upgrading to hammers and my Spearman won't upgrade to a monks staff. Now, lets take it one step further and make Unit Design more enjoyable by reducing the need to create 5 replicas of every "unit" you want.
Another issue is magic items/accessories. I have to design an archer, THEN a "Quick" archer with Belt of Initiative. Then a horse version, warg version, armored (upgrade) version, armored (leather) version, a version with cloak of shadows, a version with flame cloak, a version with ice warg cloak... it gets silly. Especially when I have to make a separate version of every troop with Amulet of Haste, Fire Amulet, Ice Amulet, Belt of Precognition...
Then I unlock the Cloaks and I have to redesign a whole new set of the same unit to add one accessory. The AI doesn't know which copy of the 19 Horse Archers to build!
The only other big unit design issue is that AI has no clue WHY I designed the troop. I designed my Fire and Ice staff users to be in a specific party with ONE heavy armored dodge high initiative troop and my Sovereign/Champion. The AI doesn't know this, so it will make stupid armies of spearmen with 1-2 staff troops - What a waste of crystal!