I disagree, medium armour isn't much better (unless I haven't found the correct medium armour yet). I got some gloves that buffed my unarmoured AC by 2, so it's equal to what I would get from half plate. Additionally I found some "barbarian style" clothing that increases my strengh by 2 which suits Karlach quite well.
Basic starter Scale Mail gives her a higher AC which is objectively better until you find Barbarian gear. Anything is better in the beginning than their starting armor and it's odd Larian makes custom stuff for them and then encourages you to ditch it.
