Yuna, like almost every other character in the game, grew up in a world in which destruction of all things, life, civilisation and hope, was unavoidable. When Yuna was seven her father died to briefly protect the land of Spira, she was exposed to ecstatic rejoicement and celebrations all around her at the same time as experiencing the agonising natural grief of losing a parent. She learned that although in this world loss and death are unavoidable, and seem to be at every turn, the fight against something unstoppable means something, that even in such tragedy there can be hope and beauty.
So, her decision to become a summoner was natural, because she realized that if she just set herself on the path to death, which she had seen all around her since she was born, she could create happiness, she could create hope, and most importantly, she wouldn’t have to see those around her die. Her mentality was that if she could give everything willingly, her life and future, it would never be taken away from her by this cruel world and she would never have to watch those around her disappear.
But in the end the girl who was willing to give everything for those she loved, just so she would never have to bear the pain of loss again, is unable to protect her heart as she always believed she would. She is spared life, and watches as once again she is subject to a loved one being torn away from her. It wasn’t supposed to be like this, she was so sure she would never have to feel this again.
That is why Yuna is a tragic figure even though she survives, that is why we should all pretend X-2 does not exist.