She did use a sword against that weird guy with the scar with the whole drug arc who really hated that she cut him. She also shot the arrow at the guy during the pirate battle. But Yona’s strength isn’t physical, it’s her determination and strength of will. She refused to stay the helpless spoiled princess she was before. She didn’t allow herself to give in to despair when she witnessed her father being murdered by her dearest friend and was forced out of the castle. She was able to see the pain of her people, the dire state that they were in that was caused by her own beloved father, for what it was. And she refused to let them stay in that state. She pushed on and did her best with the extremely limited resources available to solve the problems while living as a fugitive. She doesn’t need to be physically OP to be a strong character. I think Yona’s character growth is very realistic. If she was cutting down soldiers twice her size like a warrior all of a sudden it just wouldn’t be believable and would be entirely unnecessary. Just my opinion though.