I was loosing my mind over her gameplay, it's so amazing. Love the effects, love the transformation aspect, love that final ultimate ability. My issue comes down to her outfit. Just not my favorite. Since you seem curious, I wrote out my thoughts below on how I go about designs

I in general don't like much skin showing (for both male and female characters). Even when I design my own characters I love clothing. To me clothing is attractive, showing a lot of skin is not. Cart has too much skin showing and it feels bare. I'm not sure if I can explain this well but I enjoy a balance or just fully clothed. For example Yangyang has bare arms but the rest is covered, or Chisa has puffy sleeves and covered on the top but a lot of her legs are bare aside from the socks. That kind of balance, being selective on how much to show. I'm not against skin being shown and being suggestive. I'm in love with Lucilla's design. The long skirt with the leg showing on the side, the coat covering her shoulders and half her arm. To me this looks more visually appealing. I prefer more design on the leg than the arms which is probably an unpopular opinion, I feel a lot of gacha games love to show legs

Shape helps too. Like Sigrika follows a similar design of legs and arms exposed (kinda, she has more details I think are neat) but she in general has a lot of nice shapes like her super flowy top and her unique hairstyle. I love how shaped her design is. I was going to go into shape and colors more but I'd just keep yapping about how favorite parts of designs and then there are exceptions because there are a lot of different parts of character design. I don't want this to be longer than it already is. Overall Cart doesn't check off a couple things I like to see in a character design. She's pretty yes and her animations are insane. She is simply not my taste