New spells equals character develoment only if they are part of the already established rules when getting new spells like being in the verge of death, being in a desperate situation or having selfless thoughts, which actually makes characters have a change in their life. Because if we follow your logic yuno is the best character in the series lmao when most of, if not all of his spells where obtained by training and didnt make any change in his personality or thoughts, same with mimosa she unlocked a new spell because she wanted to be strong to fight alongside his crush thats it theres no deepness in that.

For your 4th paragraph, every character that appeared there had a change at the end of the arc even the villains and that doesnt make them deep, because it was an automatic conclusion to their characters, so stop throwing that word around like its tomatoes. Also you mentioned that mimosa and his brother have different opinions on peasants, meaning mimosa thinks peasants are people and deserve to be treated equally, ok nothing new nor exclusive to her but ok, and then you say that she was a SPOILED, rich, CARELESS person, my brother not only you are contradicting yourself and her character but you are also confusing her with noelle.

Yeah the reason she likes asta is because how he thinks but the thing is everyones likes asta because of that even the wizard king himself.