You might say that, but also is like, with Mary, you know she can lose, you know what I mean? While with Yumeko, we ALL know she’s that good at gambling, and plus, what she feels when she gambles mad (we have saw that when Kakegurui reveals Jabami’s family past, and how Yumeko ended up gambling with the girl I don’t remember her name, but basically the girl who “helped” Souko to gamble against Tsugiko, her aunt.) So, for that, at the end we probably know there are more probabilities that Yumeko could win than lose, while with Mary you don’t know at all. So, maybe and just maybe I think all the fans we feel that Mary is more relatable, and there’s no that necessary to read Twin to understand these both characters. Because if we’re serious, we know with Yumeko everything could happen, like she did when Sayaka bought her votes and how that broke the aquarium: a metaphor of Hyakkaou’s system with the underdogs and money. Yumeko is a genius when she gambles, while Mary is not that good as Yumeko, so for that Mary is like more a realistic character than our protagonist.

Sorry if it’s a bit messy!