
He's not saying she's never going to get strong. He's just trying to warn her that she might never be able to reach the duchess's level since the duchess is an anomaly. It's kind of like when people warn you about instagram models. Since they're so beautiful and popular a lot of people wish to be like them and are frustrated and sad when they can't, because in reality most of those models just re-touch their photos and stuff. I mean not really a good example but I think it kind of conveys what i mean. The knight just doesn't want her to be hurt from trying to reach for the unreachable (not necessarily true in Leslie's case) and hurt the duchess too. Just like the people who hate insta models do lol

Exactly! I also think the knight said it out of concern for the duchess as well. Since she also got hurt due to people's jealousy. The person that gave her that scar was probably someone she was close to. I don't think it was bad for Leslie to hear about this, because now she can be more careful. Imagine if she actually got frustrated over time and started to resent the duchess? That would break the woman's heart!!!
It's really pissing me off when someone tries to break people's hopes and goals before they even start ! Just let her try, become skilled and say whatever you want afterwards you dumb soldier !