What's wrong with both?
League is supposed to have a character for all types. Some people like the promiscuous types, and some like the reserved types.
Some older champions that have been sexualized in the past are also becoming a lot more reserved; Lux, for example. Akali's become less sexual (And come her eventual VGU, Nurse Akali will look like an actual doctor, like Surgeon Shen, less like a stripper nurse). Riot's implied that they want Caitlyn to be less sexual. There's Karma and Illaoi and Leona and Quinn and Irelia and Xayah (Some people get it on for Xayah, but she really is one of the more reserved champions), and yes, Taliyah.
Yeah, people like Evelynn, but it's not all just because of her sexuality, it's because Riot is really pushing the limit, here. It's different, it's new, and it's daring, it's stuff most game devs don't try to do. Yeah, games will have sexy champions, but rarely is a champion actually sexual, much less so overtly sexual that it can't help but be exciting because it's so different and unconventional.