Himuro said:
How does it go against anything the game established?
Because Squall is the protagonist of FFVIII and his story is about opening up, healing the scars of the past, and becoming a whole person after a lifetime of trauma.
Squall's whole problem is that he's the offspring of people with tragic lives and his childhood has been marked by sadness and pain; he can't trust people and he tries to hide from his own destiny.
Each of the three main sorceresses represents a different aspect of Squall's personality and he "defeats" each one in the course of becoming an actually decent person:
Edea is his "mother" and represents his anger over abandonment and loneliness; in the course of the story, he transforms her from a villain to an ally, reclaiming her motherly identity and healing the conflict.
Rinoa represents the present, friends and lovers trying to break through his shell and his fear that they'll betray him -- and therefore, his unwillingness to attach to them. Squall "defeats" this by going out on a limb and risking his own well-being and life in a desperate attempt to save her.
Ultimecia represents Squall's fear of the future and his own destiny -- the concern that his life will be terrible, that pain and suffering and betrayal by his closest allies (represented by Griever here) will be all that waits for him in the future -- and he defeats her, in one sense just by beating her up, but in another by finally allowing Rinoa's affection for him to lead him back to the present, rather than just floating off into time compression.
Given that Squall's whole character arc is about trust, it's pretty stupid if his trust actually
is misplaced in Rinoa, and especially if this plot point exists in the narrative but isn't actually addressed (i.e. Ultimecia's death never actually resolves her anger towards Squall and Squall never has to resolve loving Rinoa in the present with her horrible future destiny.) The story already has enough thematic depth without just adding things that go in the opposite direction.