Potential side reason for kayle good performence
Right now kayle main keystone is Klepto and one of the thing u get from there is skill potion. In my first game of kayle i noticed i got passive upgrade from lvl 11 at lvl 10 by using one of those potions. Basicly it's a bug that kayle passive can be upgraded faster this way and isn't tied to her lvl but the amount of leveled up skill ( same thing goes to accesint passive upgrade only after spending skill points).
Sorry for any mistakes- not a native english speaker. Rezzec