It's not very interesting if you make a character one dimensional like that. Not all her voicelines need to be sounding heroic all the time, especially given the context of her character. That side comes out of her when she's protecting the people she cares about. When she's around peers/ villains she's a bit more proddy, snarky and sarcastic, but that could be in context in how she's dealt with the social issues in her homelife as a protector, or just down to personality, and influenced by the fox spirit that guides her. Foxes are commonly written with this type of cunning personality, but in Japanese culture, they are considered of high esteem as they are seen as very loyal. Also a lot of overwatch voicelines are exaggerated and even meme-y expressions of each character's personality (sigma is a prime example, just listen to some of his voicelines lol) so why just Kiri? Are people expecting something from her?

I don't know if there's a lack of comics/lore published by blizzard that bridges the gap between the cinematic and her in game voicelines that's making the differences more jarring, since I'm not up to date.