Point relevant to the Mary Sue discussion: I (and a number of critics I follow) feel like it's a overused term as it's one nebulously defined enough to be able to be used on any character one doesn't like. For example: certain folks use the term on Rey from TFA and Diane from Wonder Woman, when both characters have serious character based flaws that effect plot. Where they are right is that these characters (and Jace for that matter) are audience ciphers, but flawless they are not.
I have stated many times that I believe Jace’s popularity (and remember in our market research he crushes the competition as the most popular planeswalker) is due in a big part to his ability to be a player stand-in.
I just don’t believe he is written as an infallible character that can do no wrong.