Y'shtola is a Mary Sue.

[Garruss]

You have to remember as well, Y'shtola is also burning her life away with her ability to see aether I would say that's a big flaw right there.

[Zabuza]

You have to remember as well, Y'shtola is also burning her life away with her ability to see aether I would say that's a big flaw right there.

Still waiting to see any consequences from that.

[AlereRaeder]

This topic is pretty cool! Shadowbringers + Endwalker spoilers
Yshtola in essence is the weakest of the Scions, sitting right next to Urianger. Both of these characters are scholars and you only really see them in the picture when there's something afoot that's not just an enemy to run at and fight.

There are many times in the story where Y'shtola is normally found in the sidelines, mutually contemplating about something or carrying out a task. I agree she's a Mary Sue in the sense where she feels more like an unkillable city NPC. But that's what Y'shtola and Urianger are. They're just scholars whose only effort in the story is the progression of the unknown, lack of better terms. They both favor the pen over the sword, so they avoid conflict firsthand. Y'shtola is never found alone unlike Urianger, she always has someone around in case she's in danger. And when she is alone, she gets kidnapped by Bowse-... Elidibus and used as bait for Mari-... the Warrior of Light, wow.

Aside from Arenvald and Raubahn losing apendages, Y'shtola is the most crippled out of the Scions. She literally cannot see, aside from aether

Still waiting to see any consequences from that.

Then you must not be paying attention to Y'shtola as a character. In the "Into the Wood" cutscene of Shadowbringers, each scion gets shot at by arrows but only Thancred has a semblance of countering. Y'shtola, Ryne, and Urianger all cower as to decrease their silhoutte size. Luckily no one is hit . And Y'shtola is visibly fighting for her life in defense against the melee attacks.

The biggest consequence is that she could not see creatures of dynamis. At the end of Endwalker:Vanaspati - Skies Aflame cutscene #2, she states:
"Y'shtola: The beast was there...and now it is no more, yes?
Y'shtola: I saw nothing. Not the blasphemy that perished here, nor the other men-turned-beasts. And because of this, I now see all too well..."

What does this mean? If there was a blasphemy right behind her, she'd be dead. What happens throughout the ENTIRE story? Y'shtola is always surrounded by the scions. She's very vulnerable. She's not a Mary Sue, she's just smart and very protected.