Y'shtola is a Mary Sue.

[Zabuza]

She's clearly weaker than us, this is a bit of a strange thing to say too when people complain a lot that she has fake died multiple times.
She failed at bringing herself out of Flow twice, failed with her shield against Zenos, failed against Emet, lies to people about her name, has to seek help from her old master even tho she's the '' master of magic '' in our group.
They also acknowledge that she's kind of an asshole in Shadowbringers too she has a major attitude problem for a while.

Yes, she's physically weaker than the frickin Warrior of Light who's the strongest being ever. I'll give you that. Still doesn't change the fact that she cannot die and emotionally/mentally is invincible. Or maybe that's going to be what the writers continue to play on? That she can't empathize with people and so acts like too much of a jerk?

It doesn't even feel like a failure when she fails the aforementioned things because she shows NO reaction to it.