Not it's that his love was superficial. .. it's more like his beliefs and logic was superficial ..
I mean it's the same with her sister ..
( Her stricking the bullies ) his old self would probably admire, but hearing what the MC said to her made him look at it differently causing him to lose interest..
Her sister is learning though, and starting to lose her naivety, I say it's better that the prince is not going to empowe that way of thinking now

I don't get this prince. He falls for the younger sister because she's a helpless doe and hated violette because she was pushy. Now the younger sister is invisible and violette is coolly polite and disinterested, and he cares? I know when ur young ur feelings are superficial but this is ridiculous.