Armors are completely out of whack in BG3.
Karlach is obviously much better off with medium armor and higher AC. But then she loses her cool unique look. Why didn't they make her custom armor Scale or Breastplate? Where are all Breast Plates and Half Plates anyway?
Same with Shadowheart. Her custom armor has inferior stats and she also loses her unique look 15 minutes into the game when you find the first basic Scale Mail. When she finally finds an upgrade to her look, it looks heavier but has the same AC. Why isn't the Sharran mail found in Grymforge a half-plate? The same level of armor Lae'zel has been wearing since level 1...
It just seems completely random and not well thought out at all.