Zero is bland but she's been in the story for less than a year.

Y'shtola has been in the game since the very beginning and she is as bland as boring as she was then. You can like or dislike the other scions but at least they had some manner of character development. Y'shtola just gained heat vision and it's only relevant when the writers say it's relevant, if not, she might as well have normal eyes. It's always so funny to me how in the scene with all the scions and Hydaelyn is saying stuff that happened to them and how they grew and then when it's Y'shtola's turn she says "uuh yes, I guess you like knowledge, keep doing whatever you are doing".