Like I said, there’s another way that a character can stop being a Mary Sue is to take them to where they’d logically go. Even if it’s not always exactly or consistently the case, it’s makes sense as to keep them from being Mary Sue. I actually think Kitty Pryde would be way less Mary Sue if they made her into an anti-heroine assassin. That’s even attempted before in Age of Apocalypse but because that storyline’s considered apocryphal, even if it’s the most realistic in the sense of taking her training and attitude into account.
(It’s like how some of the attempts to improve an existing character ends up being ‘outside’ of the main canon at times.)
Even if it’s not an entirely new take, the idea of Kitty Pryde as a leopard assassin/murderess seems to be the most logical option in line with Chris Claremont’s attempts at turning her into an avatar of a panther god and her Age of Apocalypse portrayal. Now that the female Wolverine’s role’s taken over by X23, if there’s ever a way to slot her in the assassin role I guess turning her into a leopard assassin’s the best way to go.
Or at least the closest to it.