You're forgetting that Ashe changed her ways and she realized what she was trying to accomplish was wrong. She joined Vaan's side and stopped allowing her need for vengeance control her.
Ashe was not badly written. She was a cheerful and outgoing character but after the attack on what was her entire kingdom and its people and losing all of her friends, as well as finding out her newly-wed husband with whom she was blissfully in love had been betrayed and murdered by the man tasked to protect him, she showed a side to her character that was really brave and mature. She was sad about losing her friends and people that she knew in Dalmasca; but she still managed to stand up and still be strong and awesome.
Again Ashe realized that doing things for revenge was a bad idea and in the end she tries to be a strong and confident adult and help her people break through their oppression and be a Mother type to all of Dalmasca.
Controlling your emotions demonstrably means something completely different to me than what it actually means. Meeting the man who betrayed your kingdom, murdered your husband and ultimately forced you into exile for the first time and managing to only slap him is a prime example of controlling your emotions.Again, Ashe saw what she was doing was wrong and she changed her ways.
Ashe lost all of her people, her friends, her family, her husband and her kingdom and she mostly would have seen people slaughtered and massacred right in front of her eyes. Ashe was a child queen and again she loses quite a lot of people that she knew thanks to Basch and Arcadia destroying her home. We see throughout the game that she is emotionally upset but trying to remain tough. Not to mention she feels responsible for their deaths because she couldn't stop the empire. That's a lot of trout for a seventeen year girl to go through.
Ashe becomes a Mother to Dalmasca and her people and realizes that her revenge scheming was wrong.
Ashe, despite losing her friends by a sudden betrayal and the overwhelming conquest of a much larger nation, she remains focused and brave.
Even Ashe goes through a lot of trout and I don't remember her ever acting in an unrealistic and pathetic way.
Ashe she spends like 99% of the game being a total badass, trying to free and reclaim her kingdom whilst also fighting an intense moral battle.
Even Ashe manages to move on from what's-his-name's death and Arcadia's invasion.