What makes Mia SSS top tier villainess isn't looks or her pride as a villainess (she has none): its the fact that her original personality doesn't get erased/overwritten when she gets her do-over. Sure, she grows as a person slightly, but the selfish, conceited, cowardly Mia we all know and love remains her core.
The latest bit with Chloe is pure mia: her motivation to make friends is inherently selfish (not that there is anything wrong with wanting book buddies) and thus classic Mia.
Too many "villainess gets a second chance" stories completely murder the original personality either by someone else reincarnating into that villainess or by the villainess deciding to be "kind this time" to the point where it doesn't even feel like the same person.
Here, Mia goes the "lets be kind now" route while retaining everything that makes her Mia. Its glorious and one of the heights of the genre.