Melt has one of the best glow ups in fate. Ccc she tries to break away but can't but fgo she manages to become a fully fleshed out character with her own stardom
Carrying on from her original debut, Melt is one of the characters with the most fleshed out story arc from an antagonist to a redeemed main heroine. Her figure skating theme and outfits from Ascension 1-3 also symbolize the story of the ugly duckling becoming a swan. As a Fate original character, she also didn't have the history of the usual Servant to fall back on, so that is another point for the writing.
@itsacharcoalice I know, the Sakura Five originate from Sakura (obviously). My point is that unlike most Servants, she doesn't have the real world lore and historic records to fall back on like Heracles, for example. Writing the regular Servants are easier since their backstory is all there. You just need to add the Fate spin on it. Except "looking like Sakura" Melt is essentially a blank slate, which is why I give the writer credits for making her as popular as she is.